If AC pressure switch is bad
Thread Starter
Racer
Joined: Sep 2008
Posts: 456
Likes: 0
From: FL
If AC pressure switch is bad
AC pressure switch turns radiator fan on when compressor pumps.
Switch is in compressor. (it is not high or low pressure switch)
Mine was shorted and rad. fan was always on. Advance auto offered me switch for $50 a week later. When you replace switch you lose freon. I have decided to install $3 doll relay instead.
Left diagram is original diagram, right one is diagram with new relay installed.
Note: mine is 84, don't know about another year.
Switch is in compressor. (it is not high or low pressure switch)
Mine was shorted and rad. fan was always on. Advance auto offered me switch for $50 a week later. When you replace switch you lose freon. I have decided to install $3 doll relay instead.
Left diagram is original diagram, right one is diagram with new relay installed.
Note: mine is 84, don't know about another year.
Last edited by car5car; Nov 1, 2008 at 02:45 AM.
Burning Brakes
Joined: Feb 2001
Posts: 769
Likes: 0
From: Granbury TX
I think you are working under some incorrect assumptions. Although your car is an 84 and I'm not sure of that year's system, It uses the old R4 compressor and there are no internal switches in the compressor. Also, I have never seen a pressure switch installed where you loose refrigerant when you remove the switch. All I have seen are isolated by a shraider valve under the switch, inside the A/C line. When you unscrew the pressure switch, the shader valve closes and cuts off flow. A replacement stock switch should be a hole lot cheeper than the $50.00 aftermarket unit your talking about.
Oh, By the way, having your fan on all the time (when the car is running) is not necesseraly a bad thing. I have seen many owners modify their system to acheve just that.
Oh, By the way, having your fan on all the time (when the car is running) is not necesseraly a bad thing. I have seen many owners modify their system to acheve just that.
Thread Starter
Racer
Joined: Sep 2008
Posts: 456
Likes: 0
From: FL
I think you are working under some incorrect assumptions. Although your car is an 84 and I'm not sure of that year's system, It uses the old R4 compressor and there are no internal switches in the compressor. Also, I have never seen a pressure switch installed where you loose refrigerant when you remove the switch. All I have seen are isolated by a shraider valve under the switch, inside the A/C line. When you unscrew the pressure switch, the shader valve closes and cuts off flow. A replacement stock switch should be a hole lot cheeper than the $50.00 aftermarket unit your talking about.
Oh, By the way, having your fan on all the time (when the car is running) is not necesseraly a bad thing. I have seen many owners modify their system to acheve just that.
Oh, By the way, having your fan on all the time (when the car is running) is not necesseraly a bad thing. I have seen many owners modify their system to acheve just that.
There is a second part of that story. After I installed relay everything was working well but my compressor was very noisy and I decided to install new one. I also found switch from another store and bought it. Switch looked the same but it was working like high pressure switch. So I returned it and restored my relay connection.
Arrow on the picture points at switch location. New compressor comes with aluminum plug installed in place of switch. Look at your compressor, do you have a switch there? Do you have same compressor? What year is yours?
Last edited by car5car; Nov 1, 2008 at 12:00 PM.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
That looks like the fan switch. Fan switches are a means of grounding the main relay when the pressure gets in the neighborhood of 200 psi, so it isn't engineered for the low side. Most automotive a/c systems need that 200 psi average to make cold air and to keep the Low Pressure contacts closed (so it doesn't cycle excessively). The magic number should be in your Shop Manual and a manifold gage set will tell you whether it's working right or not. On the otherhand, high pressure cutoffs cut power to the compressor clutch at 400 psi and high pressure relief valves spew refrigerant at about 600 psi. Newer stuff simply uses a thermistor like device to relay an electrical signal to the PCM proportional to high side pressure and the PCM uses that to control fan(s), high cutoff, idle, WOT and a/c (powertrain) diagnostics.
Pro
Joined: Jun 2008
Posts: 610
Likes: 1
