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

are the high/low pressure switch ok...

Jumpered the sw, no change.

manual or automatic controlls?

Also analog or digital cluster?

Analog cluster, auto. controls

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.

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!!

Replaced a/c control module,digital,changed compump.freontoo.add oil,,leak sealer. won't kickinclutch to engage.suspect short- circuit?.electrical.

1996 grandmarquis,4.6ltr.281c.i. w.

Found copy that model year repair ,troubleshoot .manual 1996merc. Grdmarquis,bookstore.