Q45 AC compressor not coming on.

[elwesso]

For a friend, not my Q.

Problem: AC compressor failed, new compressor installed and recharged to proper pressure. When you jump the compressor on the relay under the hood, the compressor comes on and blows cold air, however the compressor will not engage when the relay is in place.

[qsiguy]

When my compressor failed last year it took out the a/c fuse and gave me the same problem. Don't remember off hand if the fuse was under the hood or under the dash.

Of course make sure the pressure switch in the drier is plugged in properly too.

[elwesso]

The drier was replaced with new obviously.

[Jesda]

My 92 Q went through much of the same, fortunately they did some testing and revealed a bad pressure switch before I went and got a new compressor.

[elwesso]

Wanted to bump this....

Heres what we did.. with Diagnostic procedure 19 in the FSM, we checked part D and E..

Diagnostic procedure 19 is on page HA-85... The wiring diagram is on page HA-62-63

to reinforce the abstract on the history, the AC stopped working last fall, so this spring he replaced the AC compressor. The AC was charged properly and works fine when you jump the relay in the underhood fuse box.. so its pretty safe to say that something is telling the relay not to turn on....

Any help would be appreciated!

[qsiguy]

***(wrote this first paragraph last but moved it to the beginning because it very well could be the problem in which case you don't need to do the following troubleshooting )*************I just noticed something on the diagram and it also reminded me of something I goofed up on when I did my a/c. The "Dual Pressure Switch" is normally closed. This means it opens if pressure is too high and that happened to me. All I had to do was purge a little freon from the system and it's been working since. If you have some manifold gauges hook them up and check the pressures. You should be at about 45-50 low/300-325 high. Higher then that you need to purge a little.*************

Ok, I did some tracing of that circuit and if you can jump the relay (assuming you are jumping the ac relay) and get the AC to kick on there isn't too much it can be. Fuse is good if you can jump it and turn it on. That same fuse also supplies power to the + side of the coil. Have you tested that relay to make sure it clicks on/off? If so have you checked the contacts to make sure when it does click on/off the contact closes? If so the issue further upstream on the relay on the R/B (red/black) wire. This is the ground signal that turns the relay on/off. It goes from the relay through the "Dual Pressure Switch" then on to the ECCS Control Module.

After the Dual Pressure Switch it changes to a LG/OR (Light Green/Orange) wire all the way to the ECCS module. If you've tested the relay and are sure it's good I would go to the Dual pressure switch and check (with the a/c, car running, etc) the two wires there. The Red/Black wire is the output from the switch. Check for a ground on the Lt. Green/Orange wire. If there is a ground on that wire but not on the Red/Black wire then that switch is open. If that's the case, jumping it would turn on the a/c. If you have a ground on both sides of the switch then possibly there is a break in the red/black wire from that switch to the relay. **Noticed after writing this that the "DPS" is normally closed and I believe is a HIGH pressure switch and opens when pressure is too high.

If there is no ground on either wire then the ground signal is not getting there from the ECCS module. I would go to the ECCS module and check for a ground (again with the ac on, car running) on the lt green/orange wire on terminal # 9 at the ECCS module. If there is no ground there then I'm not sure where to go from there. You may have a bad ECCS module or the controls aren't telling the ECCS to turn on the a/c.

I doubt it's the ECCS and I think you'll probably find the problem if you trace that red/black wire all the way through the pressure switch to the ECCS.


Modified by qsiguy at 6:44 PM 4/24/2007

[qsiguy]

So Wes, what was the outcome of this A/C repair? Did you guys get it working?

[elwesso]

As far as I know he hasnt checked the pressures yet. I called him and told him about it and he hasnt responded back to me.