Ok I live in southern Texas and the summers here are unbearable and I have a 3 year old little girl who has to ride in the back, so as much assistance would be greatly appreciated. My A/C system works but I had to run wires to the compressor and the condensor to have any cold A/C, recently the compressor blew out, and I replaced it and removed the wiring I had put in place to get it to work, hoping it would work the way it's suppose to. It didnt, I took it to a friend of mine's shop sop he could take a look at it, and since I'm broke I told not to go crazy and replace everything. so here is a list of what he said was chacked and good:

1. Diode
2. Relays (all three of them)
3. Fan
4. Compressor
5. Pressure switch (sits on the condensor fan)

The mechanic said everything was fine but the system would not kick on, He said it might be possible that I have a faulty ground some where on the system but would take some time to diagnose. I checked the two grounds that I know of concerning th A/C system, thw one on tha passenger side on the fender and the one where the relay sit on top of the condensor fan. THESE ARE THE ONLY ONES I KNOW OF, PLEASE HELP!!!!!!!!!!!

 

First the obvious, fuse #35 under the hood powers the compressor and fan. The low power stuff runs off of the same fuse that runs the interior fan, so if that works can be assumed to be OK.

The command to start the A/C starts at the control panel, specifically fan switch. The fan must be on any speed not off, this grounds the small green wire. Then the signal passes to the A/C button-- if it is pressed the ground on the green wire will pass to the blue and red wire. This next goes to a thermal control on the evaporator. You can access the control by removing the glove compartment from the car (unscrew the hinges at the bottom, then pop the latch and take it out). The thermo control is a small box on top of the evaporator case with a 3 wire plug and a permanently connected gray wire. If the wire (blue/red) from the A/C button is grounded and the evaporator temperature is not too cold (clearly not a problem here) the thermo control grounds the yellow and white wire. I think the third wire on the thermo control is black/yellow, it powers the device and should be live all the time the key is on.

The yellow/white output wire is connected to the condenser fan relay. So if everything inside the car is good to go so far the condenser fan will start. The yellow and white wire also goes to the pressure switch on the high side line near the condenser. If pressure is OK, the switch is closed and it passes the signal through to the ECU. The ECU actually has control of the compressor relay. When ECU detects the signal from the pressure switch going to ground, it increases the idle speed and about 1/2 second later engages the compressor relay by grounding the black/red wire. Remember all the logic here is negative-- when wires are pulled to ground, things happen. When they are near battery voltage, the system is off.

So key things to check:
Battery voltage (from fuse 35) on the white wire at both relays (there are only 2 relays involved in A/C, those mounted near the condenser).
Battery voltage on the black and yellow of the compressor relay and yellow of the condenser fan relay with key on. This comes from the interior fan circuit.
Blue/red wire of control panel (and thermo control) goes to ground when fan switch on and A/C button pressed.
Yellow/white wire of thermo control goes to ground when fan switch on and A/C button pressed.
Condenser fan starts when A/C selected.
Engine idle speed increases when condenser fan starts.
Compressor engages.

Hotwiring the compressor straight to the battery is indeed a good way to blow it out. It is safe to hotwire the blue/red or yellow/white wires of the thermo control to ground and see if the system engages. You can drive all summer with the blue/red wire shunted to ground, all that does is bypass the fan switch and A/C button. If you have to hotwire the yellow/white to ground because the thermo control is bad, in some conditions the evaporator may freeze up on you.

 

WOW, very informative, I'll be sure to check all this when I get home today thanks.