GWR Class 165/166 air conditioning / use of hopper windows

[bramling]

But by opening the vents all you are ensuring is that the system will fail to cope.

The problem seems to be that the majority of passengers are unwilling to even give the system a chance and assume that when they step onto an A/C train and it doesn't feel like stepping into a commercial fridge it's because the A/C isn't working. And it isn't just passengers either. Relieving other drivers I have noticed that no cab is cold enough in the summer or hot enough in the winter, with the cab HVAC controls set to either full heat or full A/C.



That is a somewhat different matter. But experience shows that a system that is blowing hot is doing so because the vents have been opened.

A lot comes down to differing preferences.

Personally in winter I like heating to be on full, with windows open at the same time. This is typically what I do when I’m in my car, and some types of train like the 365 deliver a comparable experience.

In mild and warm weather conditions I’d still prefer opening windows over air conditioning, so I’m afraid I’d be one of those reaching for the windows on your 317/7s!

Even in the recent hot spell we didn’t really use air conditioning on the car, apart from on one occasion after having been cycling when I did put it on full (with windows open at the same time) for a bit just to get a blast of cool air.

One reason I’m not a fan of air conditioning is the noise it makes, which is certainly the case in confined places like train cabs. Again personal preference, but I’d take the sound of wind rushing through an open window any time. Alternatively I’d rather have complete silence and be slightly warm, than have the drone of air conditioning.

Unless there’s going to be a really decent air conditioning system which delivers fresh air and a constant 20-21 degrees even in the hottest days, few people seem to be satisfied. One more reason to use the car perhaps, where it’s easier to satisfy personal preferences - when driving alone at least!

 

[Bletchleyite]

But by opening the vents all you are ensuring is that the system will fail to cope.

The problem seems to be that the majority of passengers are unwilling to even give the system a chance and assume that when they step onto an A/C train and it doesn't feel like stepping into a commercial fridge it's because the A/C isn't working.

Which is how it is. Static air above about 22-23 degrees is horribly uncomfortable. The aircon needs to manage ideally 20-21 degrees at all times if it is to be mostly static air in the coach. If it can't it's faulty, either by design or by defect.

The issue would be helped if the system had road-coach-style (or aircraft-style) personal vents to provide moving air for individuals. I think one of the Networker classes does? Never saw it on any other train, though.

Absolutely. The key point being that the hopper windows were completely removed. Vital to prevent passengers that know best from preventing it from working!

No, the key point being that the system works properly. The Class 166 system doesn't and didn't. The system* is faulty, be that by design or by defect, if the train is not at an acceptable temperature (>=19 and <= 21 degrees in my book) whenever passengers are on board.

This "but the system" type comment is representative, as ever, of the contempt in which the railway holds passengers.

* That includes the process aspect. If it takes an hour to cool the train properly, then the train needs to have some sort of arrangement to provide that when on depot, such as a shore supply.

 

[Deepgreen]

I was thinking “hmm, in my (2007) car, the air con pump is electric” … but of course here we're talking about hardware that's over a decade older than that … so yes, makes sense I guess!


Absolutely. The key point being that the hopper windows were completely removed. Vital to prevent passengers that know best from preventing it from working!

Complete removal of any back-up ventilation? Is that really the case? If a train becomes stranded in blazing sun without a single opening window or air-con, what happens? I have a strong suspicion that doors are forced apart and chaos ensues.

 

[Bletchleyite]

Complete removal of any back-up ventilation? Is that really the case? If a train becomes stranded in blazing sun without a single opening window or air-con, what happens? I have a strong suspicion that doors are forced apart and chaos ensues.

Door barriers are provided on some trains to allow doors to be opened when there is a stranding, this is probably more effective than tiny little hopper vents which only really provide relief when the train is moving. I don't know if Chiltern have them, but equally their trains are DMUs with independently powered vehicles (so the chance of it failing on all vehicles in a train is quite low).

Of course, if trains were fitted with personal vents, it'd be easy to keep a fan going on battery power (doesn't take anything like the amount of power full aircon does) and keep people reasonably comfortable that way with no risk of them getting off and stopping the rest of the job.

 

[Deepgreen]

But by opening the vents all you are ensuring is that the system will fail to cope.

The problem seems to be that the majority of passengers are unwilling to even give the system a chance and assume that when they step onto an A/C train and it doesn't feel like stepping into a commercial fridge it's because the A/C isn't working. And it isn't just passengers either. Relieving other drivers I have noticed that no cab is cold enough in the summer or hot enough in the winter, with the cab HVAC controls set to either full heat or full A/C.



That is a somewhat different matter. But experience shows that a system that is blowing hot is doing so because the vents have been opened.

From the passengers' perspective, a very hot coach presents a choice - do nothing and hope it cools down (based on probably no working knowledge of air-con systems), or open whatever is available for some relief. Is it surprising that the latter option is chosen? Either provide an extremely reliable air-con system with only emergency opening windows that cannot easily be tampered with, or provide none and have proper windows.

 

[Bletchleyite]

I was thinking “hmm, in my (2007) car, the air con pump is electric” … but of course here we're talking about hardware that's over a decade older than that … so yes, makes sense I guess!

My car is 18 registration and I'm pretty sure it's engine-powered. So it varies by car. The electric ones do have the advantage of being able to provide "pre-cooling" in some cases. Though that's less needed in a car, as even in this present heatwave mine reaches an acceptable temperature after under 5 minutes from setting off, and in the meantime moving air is provided by cranking the fan up or opening the window, which despite this latter thing being a supposed disaster on a train works just fine, you just close it when the vents start blowing cold.

(That backs up that a system that blows hot because the windows are open is grossly flawed* in its design - it should just continue to blow cool air at maximum continuous design capacity - if nothing else, I reckon passengers would happily shut the windows if they put their hand up to the vent and felt it blowing cold)

* It was suggested above that this is due to thermostat positioning - it may well be but it's still flawed! Mind you, boiler installers do like putting heating thermostats in the hallway, the one bit of your house where you don't really care about the temperature, so clearly this incompetence pervades the HVAC industry in some form.

 

[O L Leigh]

My car is 18 registration and I'm pretty sure it's engine-powered. So it varies by car. The electric ones do have the advantage of being able to provide "pre-cooling" in some cases. Though that's less needed in a car, as even in this present heatwave mine reaches an acceptable temperature after under 5 minutes from setting off, and in the meantime moving air is provided by cranking the fan up or opening the window, which despite this latter thing being a supposed disaster on a train works just fine, you just close it when the vents start blowing cold.

(That backs up that a system that blows hot because the windows are open is grossly flawed* in its design - it should just continue to blow cool air at maximum continuous design capacity - if nothing else, I reckon passengers would happily shut the windows if they put their hand up to the vent and felt it blowing cold)

* It was suggested above that this is due to thermostat positioning - it may well be but it's still flawed! Mind you, boiler installers do like putting heating thermostats in the hallway, the one bit of your house where you don't really care about the temperature, so clearly this incompetence pervades the HVAC industry in some form.

Comparing car and train A/C systems is meaningless due to the differences in installation and usage. A car system has a much easier time of it due to have to control a much smaller environment in less taxing conditions.

I should point out that the position of the thermostats is largely due to the positioning of the A/C itself. In a car this is behind the front firewall, so it is less vulnerable to airflow coming from an open window. But for a train-based system there really aren’t many other location options, particularity for MU trains. It’s generally in the roof and nowhere else. Saying that it is flawed and should just continue to blow at maximum capacity irrespective of whatever input it receives is ridiculous.

And yes, of course opening the windows is a choice. And subverting the A/C is also a choice. But don’t then complain that the A/C is faulty because it’s now blowing hot air.

 

[Bletchleyite]

Comparing car and train A/C systems is meaningless due to the differences in installation and usage. A car system has a much easier time of it due to have to control a much smaller environment in less taxing conditions.

No, it's not meaningless, because my choice of transport is car or train. If the railway is incapable of providing working air conditioning, that's a vote for car.

I should point out that the position of the thermostats is largely due to the positioning of the A/C itself. In a car this is behind the front firewall, so it is less vulnerable to airflow coming from an open window. But for a train-based system there really aren’t many other location options, particularity for MU trains. It’s generally in the roof and nowhere else. Saying that it is flawed and should just continue to blow at maximum capacity irrespective of whatever input it receives is ridiculous.

Presumably the idea of attaching a bit of wire to it and mounting it elsewhere in the saloon is a bit too difficult? Or even a wireless thermostat, it being 2021 and all? If the passenger matters, these issues can be designed out.

And yes, of course opening the windows is a choice. And subverting the A/C is also a choice. But don’t then complain that the A/C is faulty because it’s now blowing hot air.

If the aircon is not cooling the saloon to about 21 degrees or so long after the train came off the depot, it's faulty, and so, yes, I will "subvert" it. But there is no reason it can't be made to work, because it does work in a wide range of rolling stock, and the Chiltern system proves that a retrofit can as well.

Thus, any train with poor aircon has poor aircon for one reason alone - the TOC doesn't see investing money in passenger comfort as worthwhile. So we are back to contempt for passengers. "If the wheels turn, it goes out" is not an acceptable attitude.

 

[O L Leigh]

No, it's not meaningless, because my choice of transport is car or train. If the railway is incapable of providing working air conditioning, that's a vote for car.

Fine. I’ve no problem with you making whatever choice you see fit. But saying that a train system should work like a car system at the technical level is meaningless. Your car is a sealed environment with one or maybe two people in it whereas a train stops often and the doors open and close on the outside environment as well as containing a much larger volume of air and often many more warm bodies.

Presumably the idea of attaching a bit of wire to it and mounting it elsewhere in the saloon is a bit too difficult? Or even a wireless thermostat, it being 2021 and all?

You’d have to address that question to the suppliers of A/C systems. The vast majority of systems work by sampling the intake and then deciding what to do with it next, which generally helps with design and maintenance and keeps the system reliable.

If the aircon is not cooling the saloon to about 21 degrees or so long after the train came off the depot, it's faulty, and so, yes, I will "subvert" it.

In most cases it does. That it sometimes doesn’t meet your own personal comfort levels does not mean that it is “faulty” only that it doesn’t meet what you consider to be an acceptable level. But I will say again that, based on my experience with Cl317/7s, opening the windows will only make the coach hotter not cooler because you will not only be battling what you consider to be ineffective A/C but the carriage heaters too.

But there is no reason it can't be made to work, because it does work in a wide range of rolling stock, and the Chiltern system proves that a retrofit can as well.

And the big difference between the Chiltern and GWR refits is what? And why is it that we don’t hear the same level of complaints levelled at other sealed DMU classes?

Thus, any train with poor aircon has poor aircon for one reason alone - the TOC doesn't see investing money in passenger comfort as worthwhile. So we are back to contempt for passengers. "If the wheels turn, it goes out" is not an acceptable attitude.

One reason alone…? I disagree.

 

[43096]

And the big difference between the Chiltern and GWR refits is what? And why is it that we don’t hear the same level of complaints levelled at other sealed DMU classes?

I would argue that having emergency hopper windows is a cop out that encourages slack maintenance. Having sealed windows means a/c has to be working - otherwise it gets too hot and the train gets taken out of service. That means cancellations: a language the TOC does understand as it has a financial impact.

 

[Bletchleyite]

Fine. I’ve no problem with you making whatever choice you see fit. But saying that a train system should work like a car system at the technical level is meaningless. Your car is a sealed environment with one or maybe two people in it whereas a train stops often and the doors open and close on the outside environment as well as containing a much larger volume of air and often many more warm bodies.

Then the system needs to have the capacity to provide the same level of comfort as a private car provides, if you expect people to choose rail. See also poor quality seating etc.

You’d have to address that question to the suppliers of A/C systems. The vast majority of systems work by sampling the intake and then deciding what to do with it next, which generally helps with design and maintenance and keeps the system reliable.

Domestic systems can be controlled by an external thermostat, such as a Tado system, so there's no reason a train one should not be.

In most cases it does. That it sometimes doesn’t meet your own personal comfort levels does not mean that it is “faulty” only that it doesn’t meet what you consider to be an acceptable level. But I will say again that, based on my experience with Cl317/7s, opening the windows will only make the coach hotter not cooler because you will not only be battling what you consider to be ineffective A/C but the carriage heaters too.

Do you consider an internal temperature of 25 plus degrees acceptable? I certainly don't. And much above that and you are causing a health and safety problem.

The only thing for debate is the range between about 19 and 22 degrees, really. Above or below that and it is unacceptable to the vast majority of people and so not fit for purpose. What it was designed to do is irrelevant - the point is that you need to provide an acceptable level of comfort.

And the big difference between the Chiltern and GWR refits is what? And why is it that we don’t hear the same level of complaints levelled at other sealed DMU classes

I've never used a GWR refitted unit (165s?) - I'm talking about the 166s with the original system.

One reason alone…? I disagree.

We'll have to differ there. That there are still units knocking around with non-functional ex-BR systems (e.g. most Class 158s) simply shows that the passenger doesn't matter.

 

[Failed Unit]

We are in a lovely catch 22. The 170s are awful if the air-conditioning fails, at least the 158 / 165 / 166 have an alternative. However people are too quick to open the windows. It is amazing how quickly a unit heats up in the sun at a terminal. It often takes a few minutes to cool once the engine is on again. I know airlines in other countries that shut the windows while the aircraft is on the ground to keep the cabin cool. I also recall on of the operators of mk4 (while still on ECML) asking passengers to shut the doors after them to try and keep the coach cool. That day it wasn't a fridge, but it wasn't unpleasantly hot either.

 

[Bletchleyite]

We are in a lovely catch 22. The 170s are awful if the air-conditioning fails, at least the 158 / 165 / 166 have an alternative. However people are too quick to open the windows. It is amazing how quickly a unit heats up in the sun at a terminal. It often takes a few minutes to cool once the engine is on again. I know airlines in other countries that shut the windows while the aircraft is on the ground to keep the cabin cool. I also recall on of the operators of mk4 (while still on ECML) asking passengers to shut the doors after them to try and keep the coach cool. That day it wasn't a fridge, but it wasn't unpleasantly hot either.

With 158s it works reasonably well to have the guard open the windows. The trouble with 166s on Thames Valley services is that they are DOO so getting someone to open them is near impossible. Now they are guard worked, the guard can open them if needs be so that should work.

As I said above it would be better if trains had personal vents above the seats which would still provide moving air even if the cooling failed, potentially even passively from roof "scoops".

 

[O L Leigh]

Then the system needs to have the capacity to provide the same level of comfort as a private car provides, if you expect people to choose rail. See also poor quality seating etc.

Do you consider an internal temperature of 25 plus degrees acceptable? I certainly don't. And much above that and you are causing a health and safety problem.

The only thing for debate is the range between about 19 and 22 degrees, really. Above or below that and it is unacceptable to the vast majority of people and so not fit for purpose. What it was designed to do is irrelevant - the point is that you need to provide an acceptable level of comfort.

And again, generally it does. However, you cannot cater to individual needs in terms of seating and environment when you’re providing a mass transit system. If you leave things well alone and allow the A/C to do it’s job it will get the temperature down to what most people would describe as a comfortable level.

I've never used a GWR refitted unit (165s?) - I'm talking about the 166s with the original system.

Again, not a sealed unit.

We'll have to differ there. That there are still units knocking around with non-functional ex-BR systems (e.g. most Class 158s) simply shows that the passenger doesn't matter.

With respect, you don’t know what passes within the industry out of sight of the public gaze. A lot of what happens with rolling stock, including upgrades, is the purview of the ROSCOs.

 

[43096]

With 158s it works reasonably well to have the guard open the windows.

It doesn’t work reasonably well at all. Guards are a massive part of the problem with 158 air conditioning.

 

[Bletchleyite]

And again, generally it does. However, you cannot cater to individual needs in terms of seating and environment when you’re providing a mass transit system. If you leave things well alone and allow the A/C to do it’s job it will get the temperature down to what most people would describe as a comfortable level.

Which the as-built 166 system did not do.

Again, not a sealed unit.

From experience, that is not the issue with 166s as they were when I was using them frequently (about 10 years ago or thereabouts), it's that the system doesn't work.

With respect, you don’t know what passes within the industry out of sight of the public gaze. A lot of what happens with rolling stock, including upgrades, is the purview of the ROSCOs.

I don't care* what goes on where in the industry; the industry's infighting is not my problem. What I care for is a proper level of travelling comfort being provided, else I'll simply drive.

* Well, I do, as I'm here, but the vast majority of passengers don't, and the industry has to get past this and stop making excuses.

 

[Failed Unit]

With 158s it works reasonably well to have the guard open the windows. The trouble with 166s on Thames Valley services is that they are DOO so getting someone to open them is near impossible. Now they are guard worked, the guard can open them if needs be so that should work.

As I said above it would be better if trains had personal vents above the seats which would still provide moving air even if the cooling failed, potentially even passively from roof "scoops".

Like the 365s? I am trying to think if they are the only versions of the networker that had them (but no air-conditioning) It is a while since I was last on a 16x and even longer since I was on one in the summer to care about the temperature.

 

[Bletchleyite]

Like the 365s? I am trying to think if they are the only versions of the networker that had them (but no air-conditioning) It is a while since I was last on a 16x and even longer since I was on one in the summer to care about the temperature.

Yes, I think it's 365s that have them. If all trains did, then there would be less of an issue if the actual cooling failed as passengers could still have moving air.

 

[Recessio]

They really just need to make the windows on the 165/166s actually only openable with a conductor's key, for if the AC fails. Too many times they aren't locked or as mentioned earlier in the thread, it's just a square carriage key that you can turn with a house key...

 

[Bletchleyite]

They really just need to make the windows on the 165/166s actually only openable with a conductor's key, for if the AC fails. Too many times they aren't locked or as mentioned earlier in the thread, it's just a square carriage key that you can turn with a house key...

That would be fine now they are guard operated. When they were DOO that feature was very much required to deal with yet another failure if you didn't like heat exhaustion or showing up to work looking and smelling like you'd just run a marathon.

 

[O L Leigh]

I don't care* what goes on where in the industry; the industry's infighting is not my problem. What I care for is a proper level of travelling comfort being provided, else I'll simply drive.

* Well, I do, as I'm here, but the vast majority of passengers don't, and the industry has to get past this and stop making excuses.

No, clearly. Which is why I always struggle to explain things to you. You don’t care to understand.

I mentioned ROSCOs not as an excuse or as a way of deflecting your attention, but because you say that it’s a symptom of under-investment. I respectfully suggested that you can’t know if that’s the case or not. I don’t know what actions they may or may not be taking and what obstacles may or may not be presented, and neither do you. I can imagine one which is that current A/C systems won’t fit the space available for them in legacy stock which may mean either a bespoke system may be required or more extensive (and expensive) alterations to the structure of the trains may be required.

Then, as I’m sure you’re aware, there is a squeeze going on affecting the railway’s finances. HM Government has made it clear that there isn’t a bottomless pit of money and therefore things need to be prioritised.

You may see that as excuses, and that’s your prerogative. I don’t care about that only because you, like everyone else, will make your own choices. Do I think we get everything right? No, of course not. Frankly I think we should have seen off these legacy classes long ago and replaced them with something newer, but we didn’t and this is where we are now.

From experience, that is not the issue with 166s as they were when I was using them frequently (about 10 years ago or thereabouts), it's that the system doesn't work.

Respectfully, that’s not something you could be in a position to know because…

I have certainly opened them on 166s, the aircon plain does not work. My house key fits them.

…which I have explained will do the effectiveness of the A/C system no favours whatsoever.

And in that, we come back to the beginning of the discussion all over again.

 

[WelshBluebird]

No, the key point being that the system works properly. The Class 166 system doesn't and didn't. The system* is faulty, be that by design or by defect, if the train is not at an acceptable temperature (>=19 and <= 21 degrees in my book) whenever passengers are on board.

Can't disagree with this at all.
I've been travelling a bit between Bristol and Bath over the recent hot period and IET's have been a million times better than the Turbo's in terms of dealing with the heat (so much so I've purposefully missed a local stopping service to get an IET instead for comfort reasons - which for an IET says a lot!) - so it clearly can be done!

 

[Stigy]

I was thinking “hmm, in my (2007) car, the air con pump is electric” … but of course here we're talking about hardware that's over a decade older than that … so yes, makes sense I guess!


Absolutely. The key point being that the hopper windows were completely removed. Vital to prevent passengers that know best from preventing it from working!

As far as I’m aware most cars still use the engine to run the A/C? My 69 plate car does. A pain with stop/start technology.

A lot comes down to differing preferences.

Personally in winter I like heating to be on full, with windows open at the same time. This is typically what I do when I’m in my car, and some types of train like the 365 deliver a comparable experience.

In mild and warm weather conditions I’d still prefer opening windows over air conditioning, so I’m afraid I’d be one of those reaching for the windows on your 317/7s!

Even in the recent hot spell we didn’t really use air conditioning on the car, apart from on one occasion after having been cycling when I did put it on full (with windows open at the same time) for a bit just to get a blast of cool air.

One reason I’m not a fan of air conditioning is the noise it makes, which is certainly the case in confined places like train cabs. Again personal preference, but I’d take the sound of wind rushing through an open window any time. Alternatively I’d rather have complete silence and be slightly warm, than have the drone of air conditioning.

Unless there’s going to be a really decent air conditioning system which delivers fresh air and a constant 20-21 degrees even in the hottest days, few people seem to be satisfied. One more reason to use the car perhaps, where it’s easier to satisfy personal preferences - when driving alone at least!

I understand it’s personal preference. In my car I always have the A/C on in warmer weather. In a 16x however (from a driver’s perspective) it’s so hit and miss and even when it works, it’s often not super cold (165s are arguably far better) I usually just open the cab window. In 158s the A/C is so noisy, but having the cab window open creates so much buffering it’s a a fine line with what’s better.

In 165/6s there’s no buffering whatsoever, however there’s also not a great deal of breeze when you open the cab window. They are starting to “upgrade” the AC in these units but I’ve yet to experience how effective it is.

 

[Domh245]

As far as I’m aware most cars still use the engine to run the A/C? My 69 plate car does. A pain with stop/start technology.

That's certainly my understanding, at least until the last couple of years. It's typically only been Plug-in hybrids that have made use of electric compressors, though they're also starting to appear on (some) mild hybrids

I'm curious to hear what car this is!

 

[Stigy]

That's certainly my understanding, at least until the last couple of years. It's typically only been Plug-in hybrids that have made use of electric compressors, though they're also starting to appear on (some) mild hybrids

I'm curious to hear what car this is!

I think it probably is PHEV of some sort…hadn’t considered this until you mentioned it to be honest. I’m intrigued too.

 

[Bletchleyite]

That's certainly my understanding, at least until the last couple of years. It's typically only been Plug-in hybrids that have made use of electric compressors, though they're also starting to appear on (some) mild hybrids

I'm curious to hear what car this is!

To be fair if you've already got a source of rotation and that's what you need converting it to electricity and back is fairly pointless.

 

[Annetts key]

That's certainly my understanding, at least until the last couple of years. It's typically only been Plug-in hybrids that have made use of electric compressors, though they're also starting to appear on (some) mild hybrids

I don’t know about the current range, but some Toyota hybrids have air-con that works whether the petrol engine is running or not.

To be fair if you've already got a source of rotation and that's what you need converting it to electricity and back is fairly pointless.

An air conditioning unit uses the same technology as a fridge or freezer. So operating the compressor from an electric motor is not a problem. Electric motors are very efficient and very controllable.

On the general subject of users and thermostats, many years ago I came to the conclusion that the majority of the population just don’t understand how a thermostat works. Whether for heating, cooling or both.

You often find the thermostat turned to maximum. And if you ask the user why, they tell you that turning up (or down) the thermostat produces more heat/cold. WRONG! But some people will still argue the point.

Standard heating or cooling systems either heat or cool at their rated output until the thermostat senses that the area has reached the set (desired) temperature. Then the heating or cooling will stop. Until the thermostat senses that the temperature has moved outside the set range. Then the cycle repeats.

If the heating or cooling system can’t maintain the set temperature, then the heating/cooling system will run continuously. Unfortunately with some types of air conditioning systems, they ice up and then fail to work properly if they run continuously. So if the thermostat is set to an unrealistically low temperature…

The other problem is that during hot sunny weather, especially if there is also a heat source inside the area (people, equipment), unless the capacity of the air conditioning system was properly considered, it may not have sufficient capacity to do its job properly. Then it is even more likely to fail.

BTW, each adult person is appropriately equivalent to a 100-120 Watts filament light bulb in the heat they give off. So if the area (train) is full… Add in the greenhouse effect of the sun through the windows…

 

[Domh245]

I don’t know about the current range, but some Toyota hybrids have air-con that works whether the petrol engine is running or not.

Yes, good shout. A bit of research suggests that since at least 2003 Priuses (Prii?) have had electronic compressors (apparently the industry first). Supposedly for reducing the engine load, which makes sense given the relatively limited time spent without engine running (as is my impression)

An air conditioning unit uses the same technology as a fridge or freezer. So operating the compressor from an electric motor is not a problem. Electric motors are very efficient and very controllable.

It's more a point that by going crank>belt>compressor rather than crank>belt>alternator>battery>motor>compressor you save a few % points on the efficiency. The controllability is certainly a key advantage of electronic compressors over directly driven ones, unless you start having complicated clutch mechanisms that'll slip the compressor input shaft

 

[Bletchleyite]

It's more a point that by going crank>belt>compressor rather than crank>belt>alternator>battery>motor>compressor you save a few % points on the efficiency. The controllability is certainly a key advantage of electronic compressors over directly driven ones, unless you start having complicated clutch mechanisms that'll slip the compressor input shaft

Generally cars with engine driven compressors do have an automatic clutch type arrangement (typically magnetic or solenoid driven, from a quick Google) to disconnect the compressor pump from the engine when you turn the aircon on and off (or if the refrigerant pressure drops too much). You can hear the engine working harder or less hard as you flip it on and off while idling - this wouldn't be the case if it was connected permanently.

 

[Mikey C]

My car is noticeably slower when the aircon is on. Fine when cruising, but when I want to accelerate quickly onto Motorways, I turn it off for 5 seconds