How to test A/C pressure switch
#1
08-21-2023, 09:48 PM
How to test A/C pressure switch
Greetings,
I've finished tearing out every hose under the hood and replacing them all. I now have no coolant leaks! I replaced the radiator, replaced the A/C o-rings, evacuated the A/C system and charged it.
The A/C works but the fans do not come on, so the high side pressure climbs rapidly. The fans do come on when the engine is running and gets up to operating temperature, so I know the fans work.
I suspect a bad A/C pressure switch. My question is what is the best way to test it before I plunk down another $120 for a new one?
Thanks in advance, and if anybody wants to see pix of all the hose replacement, I will start a thread on it.
PS - The car sat for 8 years in the PO's garage. The A/C blew warm when I got the car, so I have no idea if the fans worked at that time, or not. I suspect the did not, but have no proof.
I've finished tearing out every hose under the hood and replacing them all. I now have no coolant leaks! I replaced the radiator, replaced the A/C o-rings, evacuated the A/C system and charged it.
The A/C works but the fans do not come on, so the high side pressure climbs rapidly. The fans do come on when the engine is running and gets up to operating temperature, so I know the fans work.
I suspect a bad A/C pressure switch. My question is what is the best way to test it before I plunk down another $120 for a new one?
Thanks in advance, and if anybody wants to see pix of all the hose replacement, I will start a thread on it.
PS - The car sat for 8 years in the PO's garage. The A/C blew warm when I got the car, so I have no idea if the fans worked at that time, or not. I suspect the did not, but have no proof.
#2
08-23-2023, 03:45 AM
OK. I figured it out. There are five pins.
1 = ECM connection for high speed
2= Ground
3 = ECM connection for low speed
4 = Power from ignition switch
5 = A/C controller connection
With the plug disconnected from the pressure switch, you must start the car, and turn the A/C on. If you don't, the system won't "energize" and nothing will work. Once it's running you must first jumper pins 2 and 5. This is the over/under pressure control. Under 2 bar, over 30 bar the switch is open. Between 2 and 30 the switch is closed, allowing system operation. You can tell this part is working when you hear the compressor clutch engage. Then you must jumper 3 and 4. That will turn the fans on "low." Jumpering 1 and 4 will turn the fans on "high." In my case, jumpering the connector caused the fans to work. So, the switch was bad.
Technically, the switch opens a Schrader valve in the tube, so you can remove the pressure switch without losing refrigerant. However, my Schrader valve was stuck partially open. So I had to recover what refrigerant didn't escape, replace the switch and the o-ring, and recharge the system.
Maybe this will help somebody if their A/C works but the fans don't come on when running the A/C.
1 = ECM connection for high speed
2= Ground
3 = ECM connection for low speed
4 = Power from ignition switch
5 = A/C controller connection
With the plug disconnected from the pressure switch, you must start the car, and turn the A/C on. If you don't, the system won't "energize" and nothing will work. Once it's running you must first jumper pins 2 and 5. This is the over/under pressure control. Under 2 bar, over 30 bar the switch is open. Between 2 and 30 the switch is closed, allowing system operation. You can tell this part is working when you hear the compressor clutch engage. Then you must jumper 3 and 4. That will turn the fans on "low." Jumpering 1 and 4 will turn the fans on "high." In my case, jumpering the connector caused the fans to work. So, the switch was bad.
Technically, the switch opens a Schrader valve in the tube, so you can remove the pressure switch without losing refrigerant. However, my Schrader valve was stuck partially open. So I had to recover what refrigerant didn't escape, replace the switch and the o-ring, and recharge the system.
Maybe this will help somebody if their A/C works but the fans don't come on when running the A/C.
Last edited by Y2KJag; 08-23-2023 at 03:48 AM.
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#3
08-23-2023, 06:26 AM
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