1995 Grand Marquis- A/C compressor quit engaging. System charged properly, all fuses/relays OK, all grounds good, no voltage to comp.

Asked by Dec 16, 2015 at 01:19 PM about the 1995 Mercury Grand Marquis 4 Dr LS Sedan

Question type: Maintenance & Repair

A/C compressor inop. All fuses/relays OK, system charged properly, all
grounds good, no obvious damage, air gap@ comp. clutch- .002. Display on
control unit inop., all other functions operable

7 Answers

19,235

are the high/low pressure switch ok...

1 out of 1 people think this is helpful.

Jumpered the sw, no change.

6,135

manual or automatic controlls?

1 out of 1 people think this is helpful.
6,135

Also analog or digital cluster?

1 out of 1 people think this is helpful.

Analog cluster, auto. controls

6,135

Ok, so Im going to assume some things since you said that the fuses and grounds are good but some of it will be back tracking. Power flows from the cluster to the red wire pin 20 @ the eatc head, then out pin 25 purple wire to low cycling switch, then out on pink light blue wire to the high pressure switch, and on to the ac cutout relay. after the a/c cutout it has a split, one to the compressor clutch the other to the a/c diode. All of this is 12v if you have power by your volt meter or test light at the low side switch then the controll head should be somewhat functional. if there is power jump the switch and check at the high switch, if power there jump that and check power @ the cutout relay, this is where the pcm comes in by providing a signal to close the relay under normal conditions. the pcm will open the relay if it sees wide open throttle or and overheat condition. you can jump past the relay to check for power to the compressor and a/c diode. if the diode is bad it will pull power from the compressor and not allow it to work.

1 out of 1 people think this is helpful.

Thanks, Guy. I'll try all that, but It'll probably be tomorrow before I can get to it. Have some other (unrelated) fires that hafta take priority. (The fun just never stops)!! I'll post as soon as I've gone thru the steps you outlined. Thanks again!!

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