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AC blowing hot suddenly

2007 - 2014 
3K views 35 replies 8 participants last post by  HVCalTech 
#1 ·
AC blows warm/hot. Clutch dosen't engage on compressor on max a/c and highest setting with car on.
Yes ac light is on and recirculate as well, its on max a/c.
System charged properly, (cheacked with gauge on low pressure side)

I want to see if relpacing the low pressure switch solves it before taking it to a shop to be diagnosed.
Can anyone point out the low pressure switch cant seem to see where it is?

Has to be a coincidence but after installing a rear o2 sensor is when air started blowing hot. Worth mentioning.
 
Discussion starter · #4 ·
I swapped the relay with one that works and still same result. Also checked the fuses noting looks popped. Not sure which connetion to connect the multimeter to test for voltage. I see one connection plug on the compressor on the passenger side visible from the wheel well. Is it this connection or another to test for voltage at the compressor?
Also should i be doing this with the car on and ac set to max?

If the switch is bad it wont send voltage either way? correct?
 
Discussion starter · #9 ·
I'm pretty sure its electrical related because it happened the second after I plugged in an o2 sensor and started the car. I doubt the compressor just crapped out. That's why I'm asking about the switch. No one seems to be able to point out. Not sure if it's the switch by the front of the car by the abs pump or the one close to the firewall between the engine and the firewall.
 
Discussion starter · #12 ·
So the rear one is the AC cycling switch and the one in the front by the abs pump is the dual function pressure switch. Im going to check the electrical connections to the AC cycling switch later today if i can get to it from under the car. Im checking this one first because it was closest to the o2 sensor i was installing.
 

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Discussion starter · #14 · (Edited)
Thats what im thinking because I did pull the old af sensor from where the o2 is supposed to be plugged in. It caught on something while removing gently, I never pulled hard but who knows could have been enough to pull the connection loose or damage a wire.
 
Discussion starter · #15 ·
So ive changed both switches and checked all fuses and relays. Even jumped the relay for the ac compressor and clutch engages properly. I am getting power to the compressor and it spins freely. I am guessing I overcharged the system when connecting acpro to try and add freon before I replaced the switch. However the compressor never turned on when I was attempting to charge the system. Does the system pull refrigerant in with the compressor off? I am thinking maybe an evacuation and proper fill of the system will resolve my issue.
 
Discussion starter · #17 ·
Doubt you overcharged it if the compressor wasn’t running. I’m sure you got some to go in, but the vapor pressure on the refrigerant canister is only about 100 psi even at 90 F ambient temp. All that would happen is you would get some gas to go in until the pressure on the can equalized with the car’s suction pressure, which would be just the vapor pressure of the system at ambient temp since compressor is not pumping.

I think you have a wire pulled out of the connector on your pressure switch from reading earlier in the thread. If you get a connector pigtail and replace the pressure switch connector, not the switch itself, I bet it will work.
When I attempted to charge it ambient temp was about 60 degrees. Not sure if that makes a difference.

Which switch should i change the pigtail? the low pressure 3 pin switch in the front or the ac clutch cycle switch between the engine and firewall that's almost impossible to get to.
 
Discussion starter · #20 ·
Doubt you overcharged it if the compressor wasn’t running. I’m sure you got some to go in, but the vapor pressure on the refrigerant canister is only about 100 psi even at 90 F ambient temp. All that would happen is you would get some gas to go in until the pressure on the can equalized with the car’s suction pressure, which would be just the vapor pressure of the system at ambient temp since compressor is not pumping.

I think you have a wire pulled out of the connector on your pressure switch from reading earlier in the thread. If you get a connector pigtail and replace the pressure switch connector, not the switch itself, I bet it will work.
I checked the 2 pin switch ac clutch cycle between the engine and firewall and there is continuity on both pins and the harness looks fine. I will check the low pressure pigtail next.
 
Discussion starter · #22 ·
It has more to do with monitoring compressor pressures while the engine is running than fault codes.
Yeah I figured it would either give a pressure reading or something abnormal or no input at all to indicate a fault. The compressor is not coming on so the pressures are about equal 25 to 30 low and high side from the manifold gauge set I connected. I didn't want to jump the relay with the car on to force the compressor on because I don't want to mess the compressor up.
 
Discussion starter · #25 ·
Ac is now working! I brought it to a friend's shop to evacuate the system and remove any moisture and run a leak test. Then fill with correct charge. No leaks on test but only 2oz came out of the system. Which is confusing because there is no leak. It turns out it was just a coincidence with when the ac decided to stop working from low charge. I didn't disrupt anything when swapping the o2 sensor.
 
Discussion starter · #28 ·
Car was garage kept and no sign of freon loss on the floor or allover anything. I'm thinking you may be right that it was maybe a slow leak at one of the switches I replaced. Car is 15 years old and who knows how long it's been leaking or if the ac has ever been recharged. Thanks for the help everyone!
 
Discussion starter · #30 ·
So AC isn't working again. I'm guessing I've got a leak. Test with the snap on machine passed for leak test before the refrigerant fill so not sure what can be removed from the equation with that info. Maybe the Schrader valve at the low pressure fill port? I've gotta get a freon sniffer and check. I'm guessing I've gotta fill it again though to do that.
 
Discussion starter · #35 ·
Yeah I actually tried to replace just the shrader valve and it still leaked. So not sure if there was an issue with the bore or threads. Replacing the drier as a complete unit was cheap enough. Refilling with Freon a few times was not lol.
 
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