A/C Problem 2004 Pontiac GTO

rlchv70 · February 18, 2013

Working on my personal vehicle in my garage. Not a technician by trade, just a backyard mechanic. Limited experience with A/C systems.

A/C doesn't work. A/C clutch won't come on. If I command on with scan tool, it will work. However, still doesn't blow cold. I attached gauge manifold. Has plenty of low side pressure. However, high side pressure is identical to low side pressure, even with compressor on. Scan tool shows pressure sensor reads accurately.

Thoughts and ideas?

Thanks.

Keith Browning · February 18, 2013

Plenty of low side pressure is not exactly a good description... low side should be low with the compressor running and considerably lower than the high side.

Since you have a manifold gauge, what are your pressures and what is the system pressure with KOEO? The pressure number should be near what the ambient temperature number with a properly charged system is as a general rule. (at least with the Ford systems it works out that way) I suspect that your system charge is low. Ford systems won't cycle at all with low system pressure but I am assuming GM is similar. The fact that you can command the compressor clutch on with a scan tool and that the system does not cool when it is kinda backs up my guess here.

mchan68 · February 18, 2013

Just throwing a guess out there, but I vaguely recall some GM products were known to have A/C condensor leaks on a few models of that era. I would check around the outside components to see if there was was evidence of any leaks visually as a start.

rlchv70 · February 18, 2013

Some additional info:

High side and low side pressure are identical even with compressor commanded on.

Leak tested entire system with a sniffer. Replaced schrader valve on high side, but issue still persists.

I don't remember what the pressure reading was. I'll have to check my notes and reply back. It was higher than the spec for the given ambient temp.

Mbl35 · February 19, 2013

Is there a suction throttle valve at the evaporator core or somthing

that looks like an H valve used on chrysler stuff? Try whacking it with a

hammet and see if the temp drops a little.

ktmlew · February 19, 2013

GM disables compressor operation if any A/C codes are in the system. If static LS & HS pressure is in the 70-80psi range then you need to clear the codes first.

rlchv70 · February 19, 2013

No codes.

Aaron · February 19, 2013

If the pressure is the same on both I'd lean towards the A/C compressor not pumping (Shaft broke or compressor just whistled), or the restriction (orifice tube, TXV) not working.

mrbudge · February 21, 2013

If the pressures are equal on both sides with the compressor running, the compressor is nfg. I am not a GM guy, but I have seen some vehicles that you can hook up both of your guages to the same side (there are two service ports on one side) and then the pressures will obviously read equal. Even if that is the case the low side should drop and high side should rise as soon as the compressor starts, depending which side you are hooked up to. I will often do the touch test on the discharge side, if the compressor is compressing, the discharge line should be HOT.