For the first time in three years my personal daily driver vehicle has working AC! WOOOOT!!!!!!
So anyways, since I had to figure all this stuff out myself I figured I would share the information for anyone else who may be wanting to get their AC system back up to snuff.
Part 1, mechanics of how Air Conditioning works. If you understand this it makes figureing out things alot easier. Here we go.
As you all know your system houses refrigerant (either R12 or R134a). The main items of your system are the compressor, condenser, expansion valve, pressure switch, and evaporator. Basic system operation is as follows. Your compressor compresses the gas refrigerant. As you all know compressing anything creates heat. The hot compressed gas flows into the condenser where it is turned into a hot compressed liquid. From the condensor, the hot compressed liquid flows into the expansion valve where it is converted to an extremely cold un-compressed gas again. It flows through your evaporator (like a heater core) and cools the air. The cold gas is returned to the compressor to repeat the cycle. In order for this to all work, you system must be free of leaks and your pressure switch has to work. The pressure switch is the main key in engageing the clutch on the compressor.
Part 2, Electronics (Sorry G60 guys this is for SLC's but the same basic principal applies)
As I mentioned earlier, the pressure switch is the main component to making everything work. As long as there is pressure in your system, the pressure switch will close, if there is too much it will open like a fail safe. Anyways. From your HVAC controls you need to find the trigger wire. On a G60 it is Red w/ Black stripe and on SLC's it is Red w/ Blue stripe. To test to see if your connections are good on an SLC, pull the 4 pin connector on the pressure switch (Pressure switch is located next to the Driver side headlight by the radiator) and check for voltage at the Blue w Red wire. If that has power you at least know the connections and your AC relay are probably good. If not, read this page to figure out the wiring connections at your fuse box.
If you have power at your pressure switch and your compressor clucth still doesn't engage, first make sure it is connected. If it is try bypassing it. To bypass it, use a jumper wire from the blue/red wire to the green/yellow wire. If everything is connected correctly it should engage the clutch. If your clutch engages, you either need more refrigerant or your pressure switch is bad. Good news is that the pressure swicth can be repalced withouth discharging the system if you find out it is bad. If your clucth still does not engage, there is one more test before you can determine if your clutch is bad or not. Jumper the blue/red wire from the pressure switch plug to the solid green wire on your fan control module. This will bypass both the ambient temperature switch and evaporator temperature switch. If your clutch engages, you have a problem with one or both of these temperature switches. The evaporator temperature switch disengages the ac clutch if your evaporator core reaches 34 or less degrees to keep it from freezing. The ambient switch disengages the clutch if the outside temp is 34 or below to keep the compressor from freezing
The ambient temp switch is the one thats in the rain tray by the ECU. The evaporator switch is inside the car and is attached to the front (towards firewall) side of the blower box and has two small black wires coming from it. You can test both switches simply by testing for continuity. To make sure they are even hooked up at all test for continuity on the green wire at the fan control module and the green/blue (maybe green / black) wire at the ambient temp switch (with the temp sensor unpluged). If you get continuity you need to check your wiring. If no continuity, you need to check each switch individually. The ambient switch is easy. With it disconnected just test for continuity. If it's good, the switch is good, if not, you need a new one. Testing the evaporator switch is the same procedure. Check for continuity across the two black wires coming out of it. If this is bad, you need to replace it, and good luck with that one. The whole blower box has to come out and your AC system will need to be discharged.
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If they both get continuiety and you still dont have continuity from the green/blue wire to the green wire on the FCM, you have a wiring issue. If the clutch does not engage there is either a wiring problem or it is bad. I am not sure which wire does what on the compressor, but one of them should be 12v. So if all of this checks out Ok and you don't get 12v to that connector then you have a wiring problem from that connector to the FCM. If you do get 12v then the clutch is definitely bad.
Part 3 Wiring from the pressure switch.
The only two you are concerned with to make your A/C work are the blue/red and Green/Yellow. As stated above the blue/red is the trigger from your hvac controls and supplies 12v to the pressure switch. The green/yellow wire heads to the rad fan switch. From there it turns green/white and heads up to the ambient temperature switch. On the other side of the ambient temperature switch it turns green/blue and heads into the dash to connector T4a. From connector T4a it connects to connector T2b which whould have a white/yellow wire and a green wire. These two wires head to the evaporator switch. So, the green blue connects to the white yellow and goes to the evap switch where it turns green and connects to connector T4a. The green wire connects to the FCM and triggers the clutch.
I hope this information will be of help to someone somewhere down the line and if anyone with a G60 wants to contribute, feel free to let me know.
Modified by vw mofo at 10:39 AM 8-14-2003
So anyways, since I had to figure all this stuff out myself I figured I would share the information for anyone else who may be wanting to get their AC system back up to snuff.
Part 1, mechanics of how Air Conditioning works. If you understand this it makes figureing out things alot easier. Here we go.
As you all know your system houses refrigerant (either R12 or R134a). The main items of your system are the compressor, condenser, expansion valve, pressure switch, and evaporator. Basic system operation is as follows. Your compressor compresses the gas refrigerant. As you all know compressing anything creates heat. The hot compressed gas flows into the condenser where it is turned into a hot compressed liquid. From the condensor, the hot compressed liquid flows into the expansion valve where it is converted to an extremely cold un-compressed gas again. It flows through your evaporator (like a heater core) and cools the air. The cold gas is returned to the compressor to repeat the cycle. In order for this to all work, you system must be free of leaks and your pressure switch has to work. The pressure switch is the main key in engageing the clutch on the compressor.
Part 2, Electronics (Sorry G60 guys this is for SLC's but the same basic principal applies)
As I mentioned earlier, the pressure switch is the main component to making everything work. As long as there is pressure in your system, the pressure switch will close, if there is too much it will open like a fail safe. Anyways. From your HVAC controls you need to find the trigger wire. On a G60 it is Red w/ Black stripe and on SLC's it is Red w/ Blue stripe. To test to see if your connections are good on an SLC, pull the 4 pin connector on the pressure switch (Pressure switch is located next to the Driver side headlight by the radiator) and check for voltage at the Blue w Red wire. If that has power you at least know the connections and your AC relay are probably good. If not, read this page to figure out the wiring connections at your fuse box.
If you have power at your pressure switch and your compressor clucth still doesn't engage, first make sure it is connected. If it is try bypassing it. To bypass it, use a jumper wire from the blue/red wire to the green/yellow wire. If everything is connected correctly it should engage the clutch. If your clutch engages, you either need more refrigerant or your pressure switch is bad. Good news is that the pressure swicth can be repalced withouth discharging the system if you find out it is bad. If your clucth still does not engage, there is one more test before you can determine if your clutch is bad or not. Jumper the blue/red wire from the pressure switch plug to the solid green wire on your fan control module. This will bypass both the ambient temperature switch and evaporator temperature switch. If your clutch engages, you have a problem with one or both of these temperature switches. The evaporator temperature switch disengages the ac clutch if your evaporator core reaches 34 or less degrees to keep it from freezing. The ambient switch disengages the clutch if the outside temp is 34 or below to keep the compressor from freezing
The ambient temp switch is the one thats in the rain tray by the ECU. The evaporator switch is inside the car and is attached to the front (towards firewall) side of the blower box and has two small black wires coming from it. You can test both switches simply by testing for continuity. To make sure they are even hooked up at all test for continuity on the green wire at the fan control module and the green/blue (maybe green / black) wire at the ambient temp switch (with the temp sensor unpluged). If you get continuity you need to check your wiring. If no continuity, you need to check each switch individually. The ambient switch is easy. With it disconnected just test for continuity. If it's good, the switch is good, if not, you need a new one. Testing the evaporator switch is the same procedure. Check for continuity across the two black wires coming out of it. If this is bad, you need to replace it, and good luck with that one. The whole blower box has to come out and your AC system will need to be discharged.
Part 3 Wiring from the pressure switch.
The only two you are concerned with to make your A/C work are the blue/red and Green/Yellow. As stated above the blue/red is the trigger from your hvac controls and supplies 12v to the pressure switch. The green/yellow wire heads to the rad fan switch. From there it turns green/white and heads up to the ambient temperature switch. On the other side of the ambient temperature switch it turns green/blue and heads into the dash to connector T4a. From connector T4a it connects to connector T2b which whould have a white/yellow wire and a green wire. These two wires head to the evaporator switch. So, the green blue connects to the white yellow and goes to the evap switch where it turns green and connects to connector T4a. The green wire connects to the FCM and triggers the clutch.
I hope this information will be of help to someone somewhere down the line and if anyone with a G60 wants to contribute, feel free to let me know.
Modified by vw mofo at 10:39 AM 8-14-2003
