[itchyback]

Hey,
I've read the fors and againsts of each but cant for the life of me choose.
Has anyone got any feedback on reverse cycle AC in your car?
I kinda want reverse cycle, its more efficient and one less system to have in the car. but a resistence heater seems way easier to install and really i'd use it infrequently anyway.
When you were choosing, what did you choose and why?

 

[madderscience]

I think there may be one aftermarket AC/Heater system available for conversions, check places like EV West. In any case, AC is a lot harder and more expensive. Not a lot of conversions retain it. If you are going to try, best bet is keep the original car's system intact and find a way to drive it off of a dedicated motor (preferable) or your main motor's tailshaft. If the latter, you'll have a slight drag penalty from the belt at all times. You may also want to ensure the different nominal RPM of the motor (likely higher than the ICE) is taken into account when selecting pulley ratio.

Resistance heaters on the other hand are pretty easy. If your vehicle has nominal battery voltage from 96-156v you can use 120V space heater components and likely find a way to integrate them into your original heater box under the dash. If you have a 156v+ system put two 120V space heater elements in series. Use a water heater thermostat on the hot side of the element to regulate temperature, and (the only specialty part) find an appropriately rated high voltage DC relay to turn on and off the element. Make sure that it is impossible to turn on the heater element unless the fan is going and pushing air through them as well.

My original toyota MR2 conversion used (literally) a toaster for its heating element. I've also seen hair dryers used. My scion xB uses a 6-element ceramic core heater I found at a thrift shop, rewired to provide 750 and 1500w settings at 360v nominal (3s or 3sx2p).

The best type of heater to use is a ceramic core space heater (PTC heater) since these increase in resistance with temperature, providing a safety mechanism and means they work a bit better over a wider voltage range. You can find these at any thrift shop, or buy new from any home improvement or housewares place or online.

 

[e^2]

@madderscience, my diy EV came with a toaster heater too! Lol.

Good to know about the ceramic heater. I have one I was going to wire up and run on the traction batteries at 120VDC.

 

[itchyback]

Thanks MadderScience
i'll be running a 400v pack
the weather here is quite hot and in my ICE car the AC is on 9-10 months of the year. For my mind, the AC is compulsory, also, local regulations mean the heater is compulsory to defrost the windscreen, if it were for my comfort i would simply pack another coat.
I'll be running the benling compressor from EVTV straight from the traction pack for the AC. there are a few 'underdash' AC units that will do the cooling only for around $400 (Vintage Air and Nostalgic Air are two examples). So as a bolt in unit with the Benling Compressor and a reverse valve from EV Works (http://www.evworks.com.au/a-c-reverse-cycle-valve) Reverse cycle didnt seem that hard. what are your thoughts on such a system?

The other option was just adding a PTC heater as you said. Its a big energy drain and the difficulty of adding the heater vs adding the reverse valve seem comparable. Im lacking confidence, Reverse cycle AC doesnt seem like a very common choice, so i feel like i need some reassurance from anyone with feedback on such a system.

 

[madderscience]

It sounds like you've already done more research on A/C systems that I have... good call on the vintage air system though. I had forgotten about that one. From briefly looking at their site you are still going to need to figure out how to power it and where to locate the evaporator (under dash segment)

At one time I had designs of trying to adapt the refrigeration system from a refrigerated drinking fountain to make an A/C system. These are already fairly compact and run on 120VAC. I'm assuming the compressor is a sealed unit like a refrigerator, but you could power it off your suitably-oversized DC/DC converter using a regular AC inverter. the big question with that setup though would be if it would have enough cooling power to make a difference.

A window mount or portable A/C unit would be another possibility. I know from testing that the low settings on these use about 200-300W, well within the range of a DC/DC and small inverter.

 

[EVSpitfire]

Hi Itchy..
Wondering if you have had any progress with reverse cycle Air con?
I just purchased benling compressor from EVTV, Reverse valve from EVworks, but am now learning you need to deal with "Exchange valve".. a std system is single direction and need to have a Bi-Flow exchange valve. wondering if you have resolved this or any thoughts?

 

[itchyback]

Hi EVspitfire,
Thats exactly the setup i was planning. I havent progressed the idea. I was messing around with the firewall and wanted to steal 10cm from where the heater core used to be to make room for the AC.
I am also of the understanding you need two 'driers' one in the hot side and one in the cold side of the two way valve. I believe they are cheap.
I hadnt chosen a bi-flow valve, i only saw that they existed and resolved it wasnt a problem that need much attention yet. They seem pretty normal is home AC. I think a better question is finding a good AC technician who will work with you. Honestly i planned on ditching them with the problem . its one i bet theyve dealt with many times before, only now, its in a car. I was going to buy the two way valve, compressor and maybe the driers and tell them to 'make it work hot and cold'.

I havent made a final decision but had for the time being gone cold on the idea of reverse cycle AC (cough* pardon the pun). A $300 heater was an easy install and price wise, probably cheaper than reverse cycle. Mounting technical problems with driving analogue guages and gear selector through the motor controller, and my own pressure to hurry up got me thinking 'take the easy option for once!'. 40% of me just wants to do it though, screw that its harder, might cost more and is for efficiency i probably dont need. I'd feel more awesome for having done it.

Please let me know how you go!

 

[EVSpitfire]

I've now got on order a Bi Flow filter/drier (only one) which is required to replace my single direction Drier unit.
Also purchased a couple of bi flow exchange valves in different small sizes, was not off the shelf as they have never sold any this small for R134A / Bi Flow..!

One concern is whether the evaporator in the cabin, can cope with the high pressure when working in reverse mode (heating).. As the Compressor is variable speed this might need to be limited when heating ?

I'm collecting the bits now, which will take some time. Project does not really kick of till next year.

 

[EVSpitfire]

will be awhile before i manage installation
However i've bought valve and filter,
Also, concern raised on whether the evaporator can cope with high pressure (heat cycle).