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A/C Comp. Clutch doesn't engage

Nathan08T on Sat March 12, 2011 8:11 PM User is offlineView users profile

Year: 2000
Make: Isuzu
Model: Rodeo
Engine Size: 2.1
Refrigerant Type: R134A
Pressure Low: 35
Pressure High: n/a
Country of Origin: United States

This may be lengthy.. Bare with me!

Starters; I got my Rodeo at 145,XXX and the A/C did not work. I have no idea if the clutch engaged or not but the low side pressure was reading in the RED range (Don't remember pressure, just that it was high).

I bought a used compressor from someone who says it worked on his. He kept the ports clean and sealed while it was off his vehicle. It was off a 99' Rodeo with the same type of engine as mine.

I evacd my system for about an hour and leak tested it. Everything was fine. I replaced my receiver/drier and all that jaz. I installed the compressor, charged the system to about 30~ lbs and then added about half a bottle of 2oz oil. The clutch doesn't engage. I've switched out relays and nothing.

When I hook a hot wire to the clutch it starts up but I don't leave it running long enough to see if the air temp changes any. It did smell a little strange when I first did it.. But I hadn't added any oil yet (Doh'!) so I may have cut a year or so off it's life there.. I haven't hooked a hot wire to it since I added oil. I've about given up on this thing.

The compressors low side bolting was slightly different than mine. My Rodeo uses the txv instead of the orifice tube. Is it possible that his compressor came from a Rodeo that uses an orifice tube? Or would that not make any difference at all? Summers coming and I refuse to spend another 4 months without a/c!!

Thanks guy, I've been reading a lot on this forum and there's a lot of good information! Hopefully someone can chime in and help me out here.. Thanks

Edited: Sat March 12, 2011 at 8:13 PM by Nathan08T

mk378 on Sun March 13, 2011 4:25 PM User is offline

The color coded gauges can deceive you. For example they didn't have space on the can to write that it is normal to have 100 psi or so when the compressor is not running. An empty system must be charged by weight. Get a real gauge set so you can see what the high side is doing. On a TXV system, the low pressure switch cuts out below about 50 psi on the high side. Thus you need more pressure than that before the compressor will start. A pressure of 35 psi with the compressor stopped is only a tiny amount of refrigerant, not enough for normal operation. If compressor still does not engage with a full or nearly full charge, there is an electrical problem.

Also you have a potential oil issue. Too much oil can be as bad as not enough. What should have been done is to drain the oil out of the old compressor and measure it. Then drain the "new" compressor and put that same amount of new oil into it. Really I doubt the compressor needed replacing at all.

Les on Wed March 16, 2011 9:28 PM User is offline

1995 Dodge 1500 Truck V6 3.9L

pulled a vacuum on the system to 29 micron let it set 30 min. now I have the same problem as above; pressure reading on low side "60+" psi; High side is equal to low side "60+" psi. clutch will not engage, i tried bypassing low pressure cut off switch and nothing... replaced vacuum lines, and now scratching my head, wondering what I need to check now. The blower fan and thermostat seem to be working fine (not sure if that helps), oh and the relay and fuses are good, but it doesn't seem like power is getting to the clutch...

ice-n-tropics on Thu March 17, 2011 4:05 PM User is offline

Hi Les,
What is the A/C problem and service history on your RAM?
Don't comprehend your comments on A/C vacuum lines and thermostat because I don't remember that they are not part of your A/C system. Think you have a CCOT system with electric actuators.
Your Sanden compressor has a diode buried inside the wire harness close to the clutch. If the polarity is ever reversed or there is a voltage spike due to arcing or shorting or welding on the truck, the diode fails open and current doesn't reach the clutch.

Isentropic Efficiency=Ratio of Theoretical Compression Energy/Actual Energy. How To Air Condition Your Hot Rod

Edited: Thu March 17, 2011 at 4:13 PM by ice-n-tropics

Les on Thu March 17, 2011 7:12 PM User is offline

the ac was removed when i bought the truck, the only item left in the truck was the evap. I went to the junk yard; found a truck that had a full charge on the system and pulled it off. after i installed it I did a vacuum on the system and tried to install r134. Oh, I drained what oil I could from the compressor and added about 7oz of PAG 46 oil (thats all it would take).

I separated the wiring harness from the clutch to check for supplied power. Reading the volt meter; i am not getting anything to the wiring harness... that led me back to the fuse and relay (which both are good). Hmm, not sure where to trouble shoot now? any thoughts?

ice-n-tropics on Sun March 20, 2011 5:59 PM User is offline

Reply was delayed because I got sidetracked with farm land clearing and Texas Boar hunt.
Problem sounds like fuse, but you checked that. Assume that you used a jumper across the pressure switch.
To best of my recollection, clutch over-rides are
1) Wide Open Throttle (WOT),
2) High Pressure Cut out Switch (HPCOS) at about 375 psi and
3) low temp ambient (control by pressure cycling switch on accumulator, I think).
Might try clutch power presence in defrost mode.

Isentropic Efficiency=Ratio of Theoretical Compression Energy/Actual Energy. How To Air Condition Your Hot Rod

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