1986 GT the compressor and drier and tube are new. system Has full 134. if I HOT WIRE the compressor ( Both HOT AND GROUND) it blows ice cold . the "fan switch" works correctly, rad fan comes on when ac is turned on, sends power To the AC Relay (2 wires hot), BUT, Both wires to the compressor DO NOTHING. No power from green wire, And the Ground Is like it's unhooked somewhere, you cannot use the ground at the plug for a ground ! The relay is fine, I changed it out with the fuel pump, still the same thing ! WHAT can it be ??????
I believe it is A and D that are hot on the plug for the relay. the relay works fine when switched to fuel pump. but no power OR Ground getting to the plug. ( Maybe a rat chewed it ! ?
Where is the " compressor CONTROL RELAY located ??? the ground and hot wires come out of the harness Midway on the firewall below the rear window, after that it is still all wrapped up and in un -accesable places.
the Dark Green Wire is coming from "Where" ? I'm getting LOST in the middle of the page, elec cont module >>>AC control>compressor control relay where are these located ? (Inside the ECM ?) ( engine compartment , or passenger comp ?) Thanks. Mainly I just need to know exactly Where the Dk Green wire going to the Plug ORIGINATES. it shows compressor control relay, not the AC Relay, correct ? Thanks
OK - To start - a relay is an electrically controlled switch. When you send power to a relay's coil, it turns on the switch. I know - it sounds dumb at first. Why not just have the wire go directly to the compressor? Why use a relay?
The answer in this case is they want to have the ECM control the AC compressor (among other things). The ECM is too weak to control the compressor directly. So they added a relay. They are fairly simple once you think about them. So for the relay to turn on, on the coil terminals, one has to be +12 and the other ground. If both of those conditions occur, the relay will activate, it will click (you can hear it turn on) and it will allow any power the one switch contact to get to the other switch contact.
So first check to see if you have +12v on the Lt. Blue wire at the relay (with the relay removed). If not then check under the front hood where the pressure switch is if you have power on the brown wire of the Lt. Blue/Lt. Green wire connector. It's at the top of this picture.
Tht Dark Blue wire of the relay gets grounded by the ECM. If you have power on the Lt. Blue, then with the engine running, try plugging in the AC relay (ac turned on). If you hear the relay click, that indicates the ECM is supplying ground. I would have to look up when the ECM doesn't supply ground but at a normal idle it should.
If the relay is activating it should be passing the +12v from the dash (print says Brown for the wire, but I think it is Black) to the Dk. Green wire that runs to the compressor. So then pull the wire off of the compressor clutch and hook a meter to it to see if you get +12. You will have to have the key on, and I believe you will also need to have the engine running for this test. Best is to use an alligator clip wire to the connector so you're not playing around the moving belts with it running.
Finally, if you have +12 all the way down there, then look to see if you are getting a ground on the black wire of the compressor. Since that is a high pressure cut out switch, you should have ground on it at all times when the engine is off.
Overall it is not a good idea to bypass these switches. They do have functions. The low-pressure switch makes sure you don't burn out your compressor if you lose your refrigerant. The high-pressure switch turns off the compressor if the pressure builds too high, and then cycles back on when the pressure drops.
The dotted line in the relay drawing indicates that the magnetic field that the coil produces will "pull" the switch contacts closed and turn on the part of the relay that looks like a switch.
in your second picture, I don't see them, But, Mine HAS 2" Relays" in front of the windshield, next to the drier ! can 1 of these be the culprit ???? 1986 GT
One of them is the high speed blower relay. I am not sure what the other one is. The AC relay that controls the compressor is located next to the fuel pump relay in the engine compartment.
On the Compressor, on a 87GT, are the" high and Low pressure switches" Absolutely needed to be "working" for the compressor to" receive current" ? On my 85 I don't have them" in there at all" (left the plugs in) and I've had Ice cold AC for 8 years, is a 87 setup different ???
