Automotive Air Conditioning Information Forum

Ok Guys working on an 03 Chevy Suburban with front and rear ac. Last year another mechanic changed all the pressure switches compressor and a few other things I believe. I took over the position this year and now its my turn to take a swing at this thing. When I first hooked up the gauges there was approx. 5psi in the system. I evacuated that and used compressed air to fill the system and used soapy water to find that the ball valve on the high side was leaking and the schrader valve on the low side was leaking. Fixed those leaks and evacuated the system and it held 30 in lbs overnight. Charged the system today with 4 small cans of 134a or 3lbs (recommended amount) and my gauges are reading 60psi on the low side and 250psi on the high side. Which according to my chart at 85 degrees should be 45-55 low side and 250-275 high side. The vent temp is holding about 68 degrees in the front and slightly cooler in the rear at about 64-65. Also my compressor will not kick on by itself. I have to short it with a jump wire to the compressor relay. Originally I thought this was due to lack of Freon in the system but even after adding a few cans it still will not cycle on its own but turns on immediately with a jump wire. Tried switching relays that made no difference. Could the two conditions be related?

Are the inlet and outlet tubes on the evaporator the same temp. Just checking by hand should tell if they are not.

Checked it today. Coming out of the accumulator going into the evap coil I have 76 degrees. Coming out of the evap coil right next to the low pressure port I have 46 degrees.

Tim wrote:Are the inlet and outlet tubes on the evaporator the same temp. Just checking by hand should tell if they are not.

you thinking evap core tim?

No. A good way to tell a system is changed correctly is the same or different line temps coming out of the core. Should be close to the same.

With regards to the compressor not kicking on. Without a wiring diagram you're playing a guessing game. My guess is the PCM provides ground to the control side of the relay to energize it when conditions are met for the compressor to come on.

I would check to make sure there is power on the control side of the relay when the engine is running (I'm assuming you already checked the fuse?). If there is power there, I would check to see if the ground is good, I'm guessing it isn't. Provided all the connections are good and the wiring is intact, you'll have to figure out why the PCM isn't grounding the relay and allowing the compressor to kick on.

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Sorefoot wrote:With regards to the compressor not kicking on. Without a wiring diagram you're playing a guessing game. My guess is the PCM provides ground to the control side of the relay to energize it when conditions are met for the compressor to come on.

I would check to make sure there is power on the control side of the relay when the engine is running (I'm assuming you already checked the fuse?). If there is power there, I would check to see if the ground is good, I'm guessing it isn't. Provided all the connections are good and the wiring is intact, you'll have to figure out why the PCM isn't grounding the relay and allowing the compressor to kick on.


For $20 you can buy a month subscription to Mitchell DIY and get wiring diagrams and trouble shooting procedures for the vehicle. It's been money well spent for me more than once.

Awesome thanks both of you guys for the info. Messed with it a little more today and I have power coming to the relay but no ground through the pcm. So now before I go to much further on this thing I guess I need to figure out how much the boss wants to spend on it.
As for the cooling issue I noticed the compressor was really working hard when I jumped it. So now I’m beginning to wonder if there was still some trash in the lines from the last compressor and it did some damage in the system.