View Full Version : AC compressor or Expansion Valve?

06-15-2011, 09:21 PM
Ok, so I'm trying to diagnose my AC issue and I'm looking for some opinons. Here's the deal, I have a LSX swap and I'm running a 2004 GTO AC compressor. I was told the compressor had around 10,000 miles on it when it was pulled from the GTO, but I have no way of verifying this. I'm running the 240sx condenser and drier, and custom AC lines with a GM AC pressure sensor and electric fans. The PCM controls the fans when the AC is turned on and right now I have them both set to run on high when the AC is turned on.

Of course the car cools great when the temps are low around 80's or below, but on hot days I get nothing but hot air out of the vents unless I'm crusing at highway speeds. Even at highway speeds the air is blowing around 60* from the vents on a 95* day. At idle it blows more like 76*.

Tonight I hooked up some gauges to the system, because I was thinking the freon might be low, but after inspecting my pressures I'm not sure what to think. At 1000 Rpms my Low side is sitting at about 60 psi and the High side is at 200 psi. Now, when I check the FSM it tells me that if the high side is low and the Low side is high, replace the compressor. Does this sound like the issue?

Now as another issue, when I was pulling the engine last time a bolt that was holding my hoist chain broke and the engine dropped some. When it did, it bent both of the AC lines down at the firewall, which I tried bending back up and correcting. Looking over my setup with my neighbor, he thinks the expansion valve could be giving me issues or it could be the compressor. Any ideas???? I don't know if it makes a diffrence, but my car did sit for at least 4 years before I picked it up, so I don't know if that could have added to more issues. Thanks for any input.

06-15-2011, 10:05 PM
Seems like the numbers are fine considering its 95*.
High side should be 100psi above ambient temp +/-20psi. Low side 10-50psi on 75-80* day.
Did you use a AC evacuation machine and supply vacuum on the system to remove moisture?
Does it have an expansion valve or an orifice tube? Did you replace receiver/drier or accumulator?
Old ones can readmit moisture into the system

06-15-2011, 10:41 PM
I didn't replace the drier or accumulator. I'm really not sure on the expansion valve or orifice tube. The 97/98 FSM says expansion valve, but I haven't tore into it to find out for my self.
Yeah my system was vaccummed out and tested for leaks when they built my AC lines.

The FSM shows with an Ambient Air temp of 95*(F) high side pressure should be between 202 - 245 psi and low side pressure should be between 23 - 38 psi.

06-16-2011, 12:09 AM
Id say replace the accumulator for the moisture aspect. Looking at the specs for high side it should be the compressor considering low pressure on a hot day, and high on the low side. No clogged evap?

06-16-2011, 07:50 AM
if there was moisture in the system the condenser psi would be higher than normal not lower. i would say that your expansion valve and compressor are not working properly but probably neither is faulty. your expansion valve and compressor are operated by sensors (pressure and temp) and correspond to the type of evaporator and refrigerant used. if you are using a pressure sensor designed to work on an orfice tube evaporator but using it with an expansion valve evaporator that could be your first mistake. the pressure in the system is directly related to the temperature of the refrigerant when its at a vapor and liquid.