Hello! I have a 2011 GMC Terrain 4 cylinder. My AC was working last summer and this year, the compressor clutch isn't engaging. I replaced high side pressure switch as there is no low pressure switch I'm told by dealer mechanic. I've also checked fuse and changed clutch relay. I've tried to put 123a in system but it will not take any, I'm assuming it's because compressor clutch isn't kicking in. So my question do you have a way to test my clutch, I've seen videos of guys removing the relay and jumping the open pins? With car off I'm reading about 95 psi on low side? Do you have any ideas?
1st buy a set of gauges. Cheap ones will work.
Then, after letting the car sit overnight, hook up the gauges.
Don't start the car. You want to observe the "static pressure"
The Low Side and the High Side should be equal and the pressures should be close to the outside air temp.
For example. If it's 80 degrees outside, the static pressures should both be equal and around 80 psi.
Too Low and you're low on refrigerant.
Too high and the system is overcharged.
If that's good make sure the condenser fan up by the radiator is working. The condenser fan needs to work when you turn the ac on.
Lastly. You can nail this down by observing the wiring diagram.
Here you see that the ECM provides a Ground to relay socket 86 of the compressor clutch relay to energize the relay and close the contacts between relay sockets 30 and 87 when you turn on the AC (if the pressures are good).
You also need to have power at relay sockets 85 and 30 always (Grab a test light and check for that).
So if you were to take a paperclip and jump relay sockets 30 and 87 the compressor clutch should engage.
If it does, check to make sure a Ground is being provided to relay socket 86 when you turn the AC on (engine running).
If you need help identifying the relay socket numbers let us Know.
DO NOT risk jumping Power from relay sockets 30 or 85 to relay socket 86.
You'll fry the transistor in the ECM
I replaced high side pressure switch as there is no low pressure switch I'm told by dealer mechanic.
It should have some method to protect the compressor if there is too little refrigerant to keep it lubricated. Possibly the compressor itself detects that condition.
I've also checked fuse and changed clutch relay.
Did you test the clutch itself?
I've tried to put 123a in system but it will not take any
What method did you use to attempt that? (Hopefully not one of those useless and potentially damaging "recharge cans".)
Bear in mind that modern AC systems are very sensitive to even a small overcharge or undercharge. You can't blindly add refrigerant and expect a good outcome.
I've seen videos of guys removing the relay and jumping the open pins?
That can be dangerous unless you know for sure there is sufficient refrigerant in the system to lubricate the compressor.
With car off I'm reading about 95 psi on low side?
What about the high side? You can't tell a whole lot from the rest pressure unless it's very low, aside from it should be the same on both low and high side with the system at rest.
@chucktobias I've checked everything and I think it's a issue before the relay? I tried jumping pins nothing. Then I checked for power both pins on the left have power the other two on left side have no power. So from my understanding when you push the ac button it completes ground on left top pin? So I put power to the ground pin and hit the ac button and no light ?
Did you follow the diagnostic procedure posted by @jack62? Have you tested the AC clutch itself?
@chucktobias I've followed the digram I just don't understand it all. On the clutch I am not sure what pin is negative and what one is positive on 2011 GMC Terrain 4 cylinder compressor clutch
@pok3y2010 Looking at the diagram it appears there are only two connections on the compressor clutch, +12V and ground. You should be able to determine which is ground with a multimeter. (Most of the compressors I've worked with have a single +12 wire and just ground through the compressor body.) These are generic suggestions as I have never worked on a Terrain.
@chucktobias yes it's a 2 pin connector. But I read if I get them wrong I'll burn the clutch? Also the fans to cool the condenser are running at full blast is that normal?
@pok3y2010 If you disconnect the connector and attach one pin +12V and the other to ground you should be fine. It's just an electromagnetic coil. Looking carefully at the wiring diagram it appears that the ground wire is black and the positive wire is dark green, so attach power that way. You could even elect to do a continuity test first, if there's no continuity between the two pins the coil is open.
On most cars the condenser fan will run whenever the compressor clutch has power applied. In fact on my own car the AC relay is a dual-pole switch internally that energizes both at the same time.