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AC Pressure Switch Troubleshooting (SOLVED)

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16K views 6 replies 5 participants last post by  Them Witches  
#1 · (Edited)
SOLUTION AT BOTTOM. READ THIS BEFORE YOU REPLACE TXV / COMPRESSOR / PRESSURE SWITCH / CLIMATE CONTROL UNIT

I've been troubleshooting my AC for a while now, but when I was troubleshooting, I experienced new issues. This is sorta to document my troubleshooting process and also to ask for help.
I've replaced the following:
  • AC Condenser
  • AC Dryer
  • AC Thermal Expansion Valve
  • Rebuild Heater Core Assembly / Replaced Evaporator
  • AC Compressor (3 Years Old Now)
  • Various Seals
I've tested the following:
  • Fuse 14 (Under Dash) OK
  • Compressor Clutch Relay OK
  • Blower Motor Relay OK
  • Radiator Fan Relay OK
  • Condenser Fan Relay OK

There's no more leaks, which is what I started my troubleshooting journey with. It holds refrigerant perfectly fine.

The compressor clutch was working last night when I filled my AC. I put 12 oz of R-134a in, no leak sealer or unmetered PAG oil, and vacuumed out for about an hour. I didn't want to put in an entire charge to find out the compressor needs to be replaced and have it evacuated again.

This morning I started electrically troubleshooting the AC pressure switch, located in the AC Dryer. The test results were:
  • Continuity across pressure sensor OK
  • No voltage to wire 1 or 2 on the connector side (Weird)
  • 11.5 volts at connector F, wire 9 (IIRC) In Cabin Fuse Box OK
Image

Test 9 and chassis ground with your multimeter


I used a jumper wire to connect the source in the under dash fuse box directly to the pressure switch, and then jumpered the other wire to the climate control 30P connector wire 24 (BLU). Since there's continuity across the AC pressure sensor, there's the same 11.5 volts on both terminals at the pressure sensor. EDIT: This voltage was coming from Air Mix Hot, not the correct wire.

Image

Now when I turn my car to Ignition position II, the radiator fan and condenser fan both turn on. Does this mean my pressure switch is bad? My manifold gauges show 90 PSI on both the high and low side. The pressure switch activates at 28 PSI and 455 PSI, so I don't believe the pressure switch is the problem.

It's worth mentioning with the jumper connected to the Climate Control 30P connector, pin 24, and the car in ignition position II, the rad and condenser fans turn on. Switching the AC on or off doesn't change this at all. When I disconnect the jumper, the AC light turns on and off, but the fans don't turn on.

This indicates to me that the climate control AC switch is bad, but maybe the pressure switch is bad also? The clutch still isn't turning on. I'll keep testing and report back on my findings, but I'd appreciate some help here.

Test 24 and chassis ground with your multimeter

*** EDIT: This is super important, when the manual says "Wire Side of Female Terminals", that means you're looking at the terminal from the side with the wires coming out. This might be obvious to some, but it wasn't to me. Make sure you're probing the BLUE wire. The mirrored one is pink and yellow, and I'm colorblind and I was working in the dark and didn't notice.

I did end up with both of the wires going to the AC Pressure Switch / Sensor being open somewhere in their travel. I cut some jumper wire and routed them through the firewall and soldered them up and my AC started cycling normally.
 
#2 ·
I removed the climate control panel with the buttons / knobs. When I turned the car on, the rad and condenser fans didn't come on. Does this mean the button could be producing bad values that end up keeping the AC on? I'm more confused than when I started at this point, but it seems this could be a contributing factor.
 
#3 · (Edited)
Well, now that the wiring work is complete, the compressor turns on and cycles, which it wasn't doing before... but after filling the AC more, it stopped taking refrigerant at the pace it was before. The AC still does not get cold. I'm about to be busy over the weekend, but when I'm back I'll start checking the compressor and probably change the dryer - I'm sure there's a mess in there after all I've put this system through.

To summarize my symptoms, warm air (not hot) comes out of the vents. I've put in 17 oz of R-134a and the compressor cycles every couple seconds even with the doors open and fan on high, at the coldest AC setting. The condenser and radiator fan do come on, the compressor clutch engages and spins properly, the pressure moves from the low side to the high side, but it decreases more on the low side and doesn't increase that much on the high side.

I think to test the pressure switch, I can bridge the plug contacts in the pressure switch plug together to test them.

To test the AC compressor, maybe I should bridge the contacts for the clutch relay together to force it to turn on or off based on me pressing the switch. Then I could switch it manually and see if letting it run longer would do anything different with the pressure.

I think the best approach here might be the shotgun style one. I already have another AC compressor and dryer on hand. Maybe if I just order a pressure switch, I can replace it all at the same time, fill it up, and that way I get rid of all those variables at once.

Things I think it could be related to:
  • Still think it could possibly be the pressure switch malfunctioning.
  • AC compressor may be weak.
  • Dryer might be clogging the works or have too much moisture in it.
 
G
#5 ·
Hey for any of you that are using an aftermarket ecu like Haltech. To control the a/c it is the light blue wire on the back of the control unit. That goes to the pressure switch on the dryer bottle. You will need the blue wire with white stripe that comes from the bottle. That will go to your ecu so it can be controlled. I looked all over the internet for information and could not find it.
 
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