[KaspFivehundo]

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.

 

[KodiakMustang]

Not sure exactly what year your car is, but I can see by the pic that it's an early model. With the climate control calling for the a/c to be on, are you getting 12v to the compressor clutch? If not, then I'd look at the relay and fuse for the a/c. No idea if you could have popped one of those while working on the O2 sensor, but checking for the 12V will tell you if the clutch is being told to energize. If 12v is present, then maybe the clutch. No 12v, then start checking for why the power is missing. I think there is an a/c relay that some have jumped the contacts to send 12v to the clutch, and when the clutch energized, it confirmed the power was missing and the relay was the problem.

Check YouTube. I see there are some videos on there about this topic.

 

[Goose17]

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.

Please click your upper right avatar/account settings/vehicle details and enter your car year. It then shows under your screen name, which helps in conversations here. We cover multiple years of the GT500 on this forum.

Also, we encourage everyone to put their first name in their signature to make this place more friendly.

 

[KaspFivehundo]

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?

 

[Catmonkey]

Here's a couple of possibilities. While the car is moving is it still blowing hot air. If the cooling fan is not working, it's going to blow hot at low and slow speeds.

The a/c clutch is another possibility. Let the car run with the hood up and attempt to see if the the whole pulley section on the front of the compressor is turning. The a/c clutch is what it implies. If it's not engaging, it's not spinning the compressor. This is the easy stuff you can probably replace if you needed to.

 

[KaspFivehundo]

Clutch is not engaging on compressor, fan is running. It operates normally with fan speed settings its just not cooling.

 

[Risky911]

Prep yourself for about $800(just for the compressor) from the Ford dealers for a new one. They wouldn't rebuild mine and said it would cost almost as much to with no warranty on my 2010 when I had it replaced.

 

[KodiakMustang]

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?

Sorry, can't tell you exactly where to find the 12v that's telling the compressor's clutch to engage on a GT500. Did you check out any of the YouTube videos about Mustang a/c clutch problems? I bet one will tell you where to check that 12V at. I thought you might be able to replace the clutch if in fact it's bad, but @Risky911 is suggesting that's not an option. See if you can isolate the problem to the clutch first though. Then if you see voltage present but no engagement, you could verify no options are available for replacing just the clutch. Good luck!

 

[KaspFivehundo]

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.

 

[Risky911]

I'm hoping its just electrical so you can save some $$. It definitely surprised me how much a new a/c cost.

 

[SMartinez]

Your low pressure safety switch will be on the bigger of the 2 AC lines.

 

[KaspFivehundo]

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.

 

[KodiakMustang]

Who knows, maybe you’ll find a wire or plug loose close to where you were working. Good idea to return to the possible scene of the crime for a look.

 

[KaspFivehundo]

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.

 

[KaspFivehundo]

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.

 

[HVCalTech]

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.

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.

 

[KaspFivehundo]

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.

 

[Catmonkey]

I'm not sure this will help, but you can actually log a few a/c pressure sensor readings in a data log. I've used them for my a/c idle functions because there are idle parameters tied to these pressures.

 

[KaspFivehundo]

I'm not sure this will help, but you can actually log a few a/c pressure sensor readings in a data log. I've used them for my a/c idle functions because there are idle parameters tied to these pressures.

I will check that out to see if they are reporting a fault or if any reading.

 

[KaspFivehundo]

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.