I have a 2001.5 with 70k miles with an air conditioner problem. Here are the symptoms. The system has the correct pressure of r134 as checked by a cheap walmart gauge. The high pressure side metal hose doesn't get hot, and the low pressure side hose doesn't get cold or drip. The A/C fuse gets power, the A/C relay is working.

It sounds as if the compressor is never turning on, i.e. the clutch doesn't lock up. I checked power to the compressor clutch w/ the voltmeter, and nothing. The ground side of the plug still goes to ground, but I don't get any voltage between the two prongs, or between the hot side of the plug and the frame.

What controls power to the compressor? I read on here about some kind of fin probe in the evaporator. Is this common? Is there a mechanical switch somewhere, like a pressure switch, or is compressor cycling done by the computer?

Thanks.

 

add some refrigerant, I had the same problem thought it was a compresser but it was just a bit light on juice.

 

A pressure switch in the filter drier controls the compressor when the AC/defrost is on. You can jump that switch with a piece of wire in the connector for troubleshooting purposes.
Green plug in this pic:


Chris

 

Mine did the same thing. I had rubbed a hole in the high pres. line as it passes the battery box. There is a high pressure switch and a low pressure switch. I doubt anything is wrong w/compressor.

 

I've found a sharp tap with an open end wrench, etc on the pressure switch will kick start them for awhile. Then you'll know which needs replacing, easy auto parts item.

 

Please don't rely on that for correct pressures. You need to check both hi and low side pressures.

Now, that pressure switch, you can use a jumper wire between terminals to troubleshoot the switch. Don't use it as a permanent fix as that switch prevents the compressor from going kaput if the charge is lost.

 

Mine must be a little low, the compressor kicks off when the suction pressure gets down to 20psi and kicks back on when the suction pressure gets back up to around 35 psi.
As a side note, the wife's Bravada has 85lbs. suction with everything off and equalized .

 

When I charged my 96 last week the low side remained around 40-45 psi on the low side when the system had the proper charge in it (about 2.5 lbs). The compressor cycled normally at this point.

Chris

 

Ok, this is a slightly off topic but here goes......The AC on my 98.5 is charged up and works fine......HOWEVER, the compressor never stops cycling regardless of where the heat/AC controls are set....EVERY position, except the OFF position, turns the AC on and it does not matter where the hot/cold dial is set. I have no idea where to look for a problem!

Any thoughts, guys?

 

doesn't sound like you have one. the compressor on these trucks doesn't cycle on the temp dail. that only adds heat, doesn't reduce the cooling capacity.

 

seems like your symptoms and year of vehical match mine. See my post:
A/C - all of a sudden no longer cools down air - could be the evaporator due to a fundamental problem with condensate not draining adaquately, and thus rotting (leaking) out the evaporator. hope not - as the cost to repair is expensive.

A/C - all of a sudden no longer cools down air

 

CTD NUT,
I think your dash switch is where to start. It may be sticking or just be bad. It should turn off the AC compessor when in heat or vent only mode (not AC vent only). In every other position the AC compressor kicks in.

Chris

 

Stamey,

Thanks, I'll look inti the switch......I wonder how servicable it is?.....We'll soon see.....

 

CR Smith,

You should check low side pressure with the compressor running. The pressures will rise with a rise in outside air tempature. If outside air temp is around 70 degrees then you should have around 35 psi with compressor running on the low side. With the compressor off and a/c system on guessing pressure should be around 50 psi. Turn system on maxx cool, fan on high and put windows down. Put a can of 134 in your system and see if compressor starts running. This is most likely the problem, to low for compressor to cut on.

 

Please know that this is not the proper way to charge an A/C system. You need the manifold guage set so you can see both HI and LOW side pressures and get the proper charge in the system.