# Anyone direct driving (no belt) an AC compressor?



## etischer (Jun 16, 2008)

I was wondering if anyone has removed the AC compressor's magnetic clutch and connected a motor to direct drive it. I'm hoping to put an ac motor and compressor where the rear driveshaft used to be, or where the muffler used to be. Instead of the clutch cycling on and off, I was going to have the AC motor start and stop.


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## ga2500ev (Apr 20, 2008)

Just be aware that you'll still need the low pressure switch to turn the motor on and off. As the AC kicks in, the pressure on the low side drops. The low pressure switch cycles the compressor when the pressure drops too far (generally about 25 PSI). In normal systems, this cycles the AC clutch. If you remove the clutch then you are still responsible for cutting the motor when the pressure drops too far.

All of this is fresh in my head because my son and I just redid the AC in my daughter's 92 Geo Storm. It was an aftermarket install that was screwed up because the switch signal from the panel was extremely low power (like 25ma) but was trying to drive the AC clutch (which required 2.5A). So it wasn't cycling at all. I ended up routing the signal to a 2N3055 NPN power transistor that drove the coil of an auto relay, which powered the clutch from a fused line directl6 from the battery. Works like a champ now. The low pressure switch on the drier switches the low power signal.


ga2500ev


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## aeroscott (Jan 5, 2008)

ga2500ev said:


> Just be aware that you'll still need the low pressure switch to turn the motor on and off. As the AC kicks in, the pressure on the low side drops. The low pressure switch cycles the compressor when the pressure drops too far (generally about 25 PSI). In normal systems, this cycles the AC clutch. If you remove the clutch then you are still responsible for cutting the motor when the pressure drops too far.
> 
> All of this is fresh in my head because my son and I just redid the AC in my daughter's 92 Geo Storm. It was an aftermarket install that was screwed up because the switch signal from the panel was extremely low power (like 25ma) but was trying to drive the AC clutch (which required 2.5A). So it wasn't cycling at all. I ended up routing the signal to a 2N3055 NPN power transistor that drove the coil of an auto relay, which powered the clutch from a fused line directl6 from the battery. Works like a champ now. The low pressure switch on the drier switches the low power signal.
> 
> ...


glade you pointed that out and good fix . on the clutch motor mod it will save at least 10% of the power over doing a belt drive . I want variable speed drive as well ( later) . when the car is 140 deg. and I'm soaking wet hot , have the air run at max rpm so i can get cooled down fast .how fast can these pumps be run ?


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## TX_Dj (Jul 25, 2008)

Scott,

Based on what I've read (admittedly not much) the compressors can run up to the max ICE redline, but what is the ratio difference between the crank pulley and the AC pulley?

Also, what I've read, is that the compressors are typically most efficient around 2500 rpm at the compressor.

This is why I was searching for a pack-voltage motor around 2500 rpm with enough gusto to keep the compressor turning at rated speed. Direct-drive is definitely the way to go, as far as keeping losses down.

To the OP, you'll certainly need a stable shared platform that both the motor and compressor attach to (to prevent any flexion that could put undue stress on either device's bearings) and probably some sort of keyed/taperlock something-or-other to keep the two devices attached at the shaft.

Shouldn't be hard to do, but will require a little conscienscious engineering.


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## 1clue (Jul 21, 2008)

Save yourself some pain in this, and put in a flexible shaft coupling.

http://www.mcmaster.com/ go to page 1145. You can pick these things up at any HVAC shop, any farm supply or most hardware stores. Go to the electric motor section and they'll be on a wall, they're cheap.

You still want to align things as best you can, but this setup will be quieter and more reliable than a direct "hard" coupling since it won't stress the bearings on either your motor or your compressor.


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## etischer (Jun 16, 2008)

I would definitely not try to run a direct hard coupling. I was wondering what an AC compressor looks like with the clutch disconnected. Is it some funny flange I would have to make an adapter for or would it be a standard shaft?





1clue said:


> Save yourself some pain in this, and put in a flexible shaft coupling.
> 
> http://www.mcmaster.com/ go to page 1145. You can pick these things up at any HVAC shop, any farm supply or most hardware stores. Go to the electric motor section and they'll be on a wall, they're cheap.
> 
> You still want to align things as best you can, but this setup will be quieter and more reliable than a direct "hard" coupling since it won't stress the bearings on either your motor or your compressor.


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## aeroscott (Jan 5, 2008)

TX_Dj said:


> Scott,
> 
> Based on what I've read (admittedly not much) the compressors can run up to the max ICE redline, but what is the ratio difference between the crank pulley and the AC pulley?
> 
> ...


thanks , i missed your post . that would mean i crank this thing up for very fast cool down . I'm thinking that battery temp control will be added later to get best battery life , performance . I wonder what hp a ac pump running at max rpm and pressure will need . with a reversing valve (4 way ) you'd have a kick a-- heater , almost instant on heat pump . A little insulation for everything , I bet I can get a nap in the hottest weather for less then 100 watts / hr. and if I dared to use ammonia it could be 50 watts / hr or less .


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## piotrsko (Dec 9, 2007)

back in the day...... on V-dub beetles, there was an a/c option that nobody hardly purchased because it took 15 hp to run. with the A/C running a bug wouldn't get usually more than 35/40 mph. I'd figure at least 10 hp for starters. 

I'd also go 5,000 rpm motor or faster and reduce the shaft speed by gearing so it would draw less power.


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## rich18325 (Aug 17, 2008)

Hey There are couplers used in industrial applications brand named lovejoy.If you ask for it by this name most belt and bearing supplers will know what you need ,it maybe another brand. this type of coupler is very forgiving for alanment and has 2 steel ends and a rubber piece in the middle to absorb vibrations. you can use the part of the clutch that is attached to the a/c shaft and cut away the outer flange leaving the center. Get a coupler to fit the motor and bore one end to fit the outside diamater of the center piece less .003 in. drill a hole 90 degrees to the bore in that end. chille the center piece in dry ice .with a press push it in the coupler end. this is called an interference fit. weld the drilled holes on the side and it will nevecome apart. install it on the shaftwith the orginal nut. you will need some help of someone with a lathe. Hope this helps Rich http://www1.mscdirect.com/cgi/nnsrhm page 3817


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