need GN a/c guru

[Warped]

We're on a streak of 100* days in Texas and I'm just getting around to addressing the A/C that hasn't worked since last year. The GN is a daily driver again so I'd prefer to have the A/C working. I had it evacuated and charged in 2009 and it lasted about a year.

With engine running, AC on and blower on high the compressor clutch does not engage. Direct Scan shows A/C is set to on from the ECM. With the compressor not engaged the high and low side pressure is reading 110. I hot wire the compressor per the manual and the clutch engages and low side pressure goes down to 45 and the high side goes to 245. Those numbers appear to be about right in the manual. It seems to be cooling some when I hot wire it but I'm reluctant to leave it hot wired long enough to see how much it will cool. Need an expert's opinion on this. We're melting down here. Thanks.

 

[SHADOWII]

Not an expert....

however, leave it hot wired and measure the temp coming out of the vents. If you are getting cold air<50*, the issue may be w/the ac controller,
harness(?) or relay.

 

[Sal Lubrano]

What did you do? Bring 12 volts to the compressor? If so, return everything to normal. Place a jumper in the low pressure cycle switch on the accumulator/drier, if the compressor runs then that switch is bad.

 

[Warped]

Sal,

I forgot to mention a few things as will happen when you try to work on a GN at midnight. I had scraped off some insulation from the hot lead to the clutch so my tests were run with the wiring connected. Used a test light to check for power to the clutch and there was none. Connected the jumper to the hot wire where I scraped the insulation away and it ran.

Also, I did jump the cycling switch and the clutch still did not engage. I rechecked that again this morning and the it does not engage.

So it sounds like you think the freon level is ok and I need to go back to the manual and track down yet another electrical gremlin.

I really appreciate all your ideas and tips. It's a lot easier to learn from someone who's had experience with these things. Thanks.

 

[Sal Lubrano]

If i remember correctly the cut in pressure is about 45psi. (You have 110psig, so you are good there) If you have more than 45psig on the low side, the low pressure switch will make completing the circuit to the compressor. If you jumped that switch and the compressor does not go on then you have either a bad compressor clutch (you tested for that already by putting 12 volts directly to the compressor) or a power issue, wiring, fuse, bad selector switch (don't think so since the ecm sees you calling),or high pressure cut out switch.

 

[Sal Lubrano]

double post

 

[Nick Micale]

......... low side pressure goes down to 45 and the high side goes to 245. Those numbers appear to be about right in the manual. It seems to be cooling some........... Thanks.

The low side should pump down to 25-30 psi, and high side ~300 psi.

To me, is appears you are low on freon, or possibly the compressor is bad.

This is a guess of course, since information is missing like what engine RPM when checking, do the numbers fluctuate and other factors.

 

[charlief1]

First dumb question. Is it R-134 or R-12?

Second dumb question. Feel like driving to Hillsboro tomorrow for me to take a look at it?

 

[GNRick]

First dumb question. Is it R-134 or R-12?

Second dumb question. Feel like driving to Hillsboro tomorrow for me to take a look at it?

Hey Charlie! We already know the answer, don't we? It's the green wire from the switch on the drier to the compressor!

 

[charlief1]

Hey Charlie! We already know the answer, don't we? It's the green wire from the switch on the drier to the compressor!

Possible Rick but I walked you through it.:smile: Since he's just a little bit from me (Texas wise) I'd prefer to have him come so I can help him out.:smile: Bring a 30 pack and I'll start the grill/smoker up.:biggrin:

 

[GNRick]

Any updates?