# AC Revisited (the cold kind ;) )



## ElectriCar (Jun 15, 2008)

I've heard the figure of 1.5HP. Remember ICE hp is much less in an electric motor ie 1HP electric = 7-10ICE HP or so I've read.

I'm thinking the window unit compressor may not take the abuse of constant jarring in the automotive setting as well.

I've got my compressor set aside for now but I'm planning to put a motor of some type on it. I've just got to find a motor controller to handle 156V.


----------



## TX_Dj (Jul 25, 2008)

I was concerned about the window unit compressor's durability as well, but if I could find one cheap enough, and if it would work as well or better, then I was considering giving it a try, just to see.

Another reason I wanted to try it is because I expected since it's designed to run at one speed, it would run at the most efficient speed to work with the rest of the system.

I wonder if anyone knows where to find technical data on automotive AC compressors to determine what their peak efficiency RPM is, and how much power it really takes to move it at that speed. If one could find a PM motor of the right power and RPM to make that happen, you could just turn it on and off without having to control its speed.

Of course if I had a speed controller, I could slow it down when it's getting too cold and still maintain the cool without such a high drain on the power reserves. Hmmm!

Oh my, what am I getting myself into.


----------



## aeroscott (Jan 5, 2008)

hermetic pumps (window units)put all the motor heat into the refrigerant . so there is some loss thier . but they are pretty good , some small twin engine airplanes run hermetics / inverter units ,heard they work great (better then the open/ auto type units they replaced) so I go back and forth .I 'm also thinking of battery temp management (bigger load ) . the best should be a open /auto unit directly driven by ( no belts / chains ) high voltage vfd so speed can match load . part of the load on a ice car is the huge heat load of the engine 200,000 to 500,000 btu i would think it would be good to put the condenser at the back of the car so heat goes up and behind . if we could use ammonia
in our units it would consume 5 times less power . a small window unit at 500 watts would be 100 watts .
to add to the power saving we can spray water on the condencer at 8000 btu / gallon that should save about 600 watts .














9


----------



## Qer (May 7, 2008)

It would be pretty simple to do a small PWM-controller to run any DC-motor with a voltage lower than the pack voltage though. There's a thread about someone that found a 555-based little PWM-unit as a kit, that would work.http://www.diyelectriccar.com/forums/showthread.php?t=17913


----------



## Telco (Jun 28, 2008)

I've also considered a window unit as an AC unit. Looked at one at the store though, and the freon piping is tiny, like 1/4 inch. Those units also use a different freon than automotive applications. 

If you were to use one for parts, you could easily replace the evaporator in the existing system, would need all new plumbing. The condenser for the window unit could be installed in front, but would need modification as it's designed to fit 3 sides of a box. It would also need to be protected as it's not designed to take 70MPH rock and bug impacts. The automotive condenser MIGHT work, no idea as to the effect that going from a small diameter pipe to a larger diameter pipe, then back to a smaller diameter pipe would be. The rest of the unit would also need to be used, but could be packaged anywhere in the rig. You'd also have to find an HVAC guy willing to draw down and recharge the system with a non-automotive freon, which will probably be hard to do since the EPA would likely come down hard on them for it if they found out. They might even think YOU are an EPA guy doing a sting.

An alternative to all this that I was considering was installing a window unit in the bed of my truck. If I were to go this route, the bed would be cut out, and a hole would be cut into the cab of the truck. There would be a shelf attached to the cab for the window unit to mount to, ducting to bring air into the body of the window unit from the outside for cooling, and rubber isolators to keep the unit from being beat to death. The unit would then be upholstered in to look like it belonged, and all the existing AC stuff would be removed. The bed would also be welded back over to form a cover over the unit, and to make the bed usable for most things again. I really only see this working on an extended cab truck though.

The factory AC needs to spin at about 2000RPM for best effect, this would be about the equivalent of the engine running at 1800RPM. But, to determine the actual RPM that would be needed, drive the car and find what speed gets you the coldest air. Might need a thermometer to determine this. Once you have this, you can measure the crank pulley diameter and the AC diameter, and figure the actual compressor speed from this. To figure this, measure the pulley diameters, multiply each by 3.1416, divide the crank pulley answer by the AC pulley answer, then multiply engine speed by the answer. Need a math guru to check my procedure on this though. A 2HP motor should be plenty for this. 

If you want to use an electric motor to drive the compressor, you might also consider running the power steering pump and a small 12V alternator off the ckt as well. I suggest the alternator to run the 12V systems in the car, and it need not be a big one since 60 percent of the alternator's load will no longer be present. I'd suggest this instead of a separate converter to get 12V off a battery pack, since you'd be running a motor to run these systems anyway, and a 120V 3HP motor is going to be a LOT smaller than a 12V 3HP motor. These aren't necessary suggestions though, just thought I'd throw them out there.


----------



## skullbearer (Jul 9, 2008)

I can already see a few problems I need to point out ASAP with what you said Telco.

If you go from a small diameter pipe into the large diameter condensor, your freon will cool proportionally to the change in volume, and you will have a very cold condensor which is actually heating the freon rather than cooling it, or at best slightly cooling it. When it hits the small pipe again it will become heated once more and you will have a heating system which draws heat from the outside air essentially. More like a lukewarm system.


All AC systems are primarily vacuum inside, if you overfill one to eliminate the cooling effects of the change in diameter pipe, then you will get liquid freon into your compressor and blow it.


CONDENSOR RPM: As for this, the optimum speed is considered engine speed of 2500rpm, this is the industry standard for testing, and in older R12 systems properly maintained, you could sometimes actually make frost in the vents, its pretty sweet (only with deionized water, tap water freezes at a colder temp than 'water' due to minerals and other chemicals).

To test your system, particularly if you are running it with a separate non-drive motor, you can setup a big room fan infront of your grill to blow over the condensor, run it at 2000-2500rpm (check to make sure there was no gearing ratio between the engine and compressor speeds, there are some cars that use a reduction to get less or more compressor rpm at 2500 engine rpm). Stick a basic thermometer in either center vent, those get the most direct airflow. Run it on 'max A/C' or top vents, recirculation, maximum cold, on the highest fan setting.

It should get about 36-40degrees for an R134a system, and 33-37degrees for an R12 system.


FREON: Running anything other than R12 or R134a (as determined by the system's design and hosing) in a vehicle is ILLEGAL. EXCEPT when you use freon mixes, which are required to be classified and the vehicle labeled, which means you are stuck with one shop and one shop only, since they usually make their own mixes to guarantee you have to go to them. DONT GET A MIX!

DO NOT buy freon with stopleak, DO NOT use the cheap AutoZone plastic guage/filler tools, and DO NOT just add freon until it gets cold. If you make a custom system, install a viewer window in it or get a Reciever/Dryer with a view window. Basically you will add freon until you start to see it rushing past in the window, then VERY SLOWLY add more freon until it just barely goes 'filled' with freon. DO NOT ADD MORE at that point, let it run, see if it starts to get streaky again or not.


NEVER NEVER refill a system by venting freon into the air, one system's worth of freon is like a year's worth of driving in terms of damage to the environment. Not to mention it is a massive fine and jail time if you are reported. Take it to a professional who will use a leak detector and a recovery/fill machine to remove the old freon, and add new freon with the appropriate amount of oil.


The amount of oil is proportional to the freon requirements of the vehicle + oil need of the compressor. Over oiling is bad because it prevents the freon from working, under oiling is bad because it will cause your compressor to sieze. Often in days.


The best A/C systems (mechanically) have a second metering device just after the evap but before the compressor, which restricts or unrestricts flow based on the temperature of the freon. Hotter means more gas is coming out of the evap and so it is safe to allow past at a higher rate, cooler means less gas is coming out, and the rate needs to be decreased to prevent liquid from leaving the evap. If liquid freon reaches the compressor, BAM! Have to replace your compressor, your condensor, possibly your oriface or TEV, and even worse maybe your evap too. That's the whole system!


The good thing about the metered flow systems, though usually only found in high priced luxury cars, is that they run a smaller compressor 100% of the time the A/C is on. Rather than metering by shutting the compressor on and off, the thermal meter does it, and you get a much higher system efficiency and much colder air. THAT is the kind of system that (with R12) can make frost. Had a good frost maker in an 86 Toyota Cressida Sedan. Thermally metered R12 system, I fixed it up, filled it proper with R12 (which requires you to be working at a shop, at a school shop, or own a licensed shop, and to half a freon handling license of your own... thankfully my teacher did because I have the license but didn't work at a shop). That thing would freeze out the back seat, and forbid you were in the line of vent fire, your nads would drop clean off in half an hour.


----------



## TX_Dj (Jul 25, 2008)

I'll be first to admit- I never finished my automotive AC certification... so what little I know came from that education, and since I was never tested on it- what I know may be wrong. 

And of course you found the nugget I wasn't considering, skullbearer- the heat/cool happening from the diameter change from the smaller sized compressor and the larger diameter components in the car.

But, you bring up a good point- in order for me to convert the window unit to R134A, I would have to have it purged, flushed, and draw a vacuum on it... and I don't have the equipment or license to touch R12, so I couldn't prep it in accordance w/ law.

I think I'll settle on a belt-drive for the compressor, with a dedicated motor. I wonder which would be less efficient, a flat grooved belt like from a serpentine system on an ICE, or a cogged belt like from a motorcycle belt drive. I could get a 2500 rpm-ish motor and 1:1 pulleys and use the shortest belt possible.

Still a long way away from that, but I think once I do, I'd like to put it and my vacuum pump in a recessed truck box that I can mount with rubber isolators and put some sound deadening insulation into so that I can reduce or eliminate the vibration and noise from those two items.


----------



## ElectriCar (Jun 15, 2008)

What about the Pruis AC motor/compressor? Aren't they a hermetic unit? But if the motor is 3-400VAC that wouldn't work for 6V battery users like myself. 

I'm wanting to use a 156V system for a little better pep in my S10. Common industrial motor specs are 90 or 180VDC at 1750 rpm. These could work but what type controller would work? Unlike an AC motor, DC motors can't be oversped without field weakening unless you over volt. In my case I suppose I'd have to use a 90V motor and overvolt it to about 125V to get the rpm's. 

Anyone know if 1HP is enough to drive the factory compressor at 2500rpm or 1.5HP? I've read somewhere that it should be one or the other.

Now I just had an idea. To use a heater core from a 120V heater, I'd need to limit the voltage to 130V or so as well. If I find a contorller to run on 156V I could use it to power both the heater and AC motor!

What can I use for a controller to operate with a 156V pack???


----------



## morvolts (Jun 19, 2008)

ElectriCar said:


> What about the Pruis AC motor/compressor? Aren't they a hermetic unit? But if the motor is 3-400VAC that wouldn't work for 6V battery users like myself.
> 
> I'm wanting to use a 156V system for a little better pep in my S10. Common industrial motor specs are 90 or 180VDC at 1750 rpm. These could work but what type controller would work? Unlike an AC motor, DC motors can't be oversped without field weakening unless you over volt. In my case I suppose I'd have to use a 90V motor and overvolt it to about 125V to get the rpm's.
> 
> ...



I believe the Prius is 208VAC.
From the one I saw locally that someone is trying to adapt it looks like its going to need a complicated controller to work.Still a nice package if someone can sort it out.


----------



## TX_Dj (Jul 25, 2008)

Yeah, in my case I just want a motor I can turn on or off. All or nothing. I don't need to spend lots of money or sacrifice more weight to a controller.

Either it will run fine on 12v or it will run fine on 144v, or I'll find another way to do it.

Same is true for heat.


----------



## aeroscott (Jan 5, 2008)

[LEFT said:


> *skullbearer*[/LEFT];61503]I can already see a few problems I need to point out ASAP with what you said *Telco*​.
> 
> If you go from a small diameter pipe into the large diameter *condensor*​, your freon will cool proportionally to the change in volume, and you will have a very cold *condensor*​ which is actually heating the freon rather than cooling it, or at best slightly cooling it. When it hits the small pipe again it will become heated once more and you will have a heating system which draws heat from the outside air essentially. More like a lukewarm system.
> 
> ...


good post , some systems run a receiver after the evaporator , would that do the same as the metered flow . on the ozone damage it states on the EPA test it's only a theory ( a weak one at best ), but it's law .word was *DuPont's*​ r-12 patent had run out .on tubing size everything on the high pressure side of the expansion valve is low flow high pressure like kinda like a *accumulator*​ ( not much pressure drop )


----------

