A/c Problems - 2010 Mustang Gt

Dak

New Member
Apr 3, 2015
5
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1
Gilbert, AZ
Hey everyone! I'm new to the forums, so you'll have to excuse me for any forum rules until I've explored, as I know a lot of them are really specific with what you can post and where and what not.

I'm at a complete loss with my A/C on my 2010 GT, and am not willing to hand over $100 to Brake Masters for "further electrical diagnosis" after they gave me the run around.

In a nutshell, last summer my A/C was evapped/recharged. Everything worked flawlessly. However in Arizona the Summer comes around a lot sooner than for most and a few days ago it was one of those 95 degree days already and needed to kick on the A/C for the season for the first time. Blew fine, but did not get cold at all.

The only thing I changed on the car this Winter that would've had an effect on the A/C compressor possibly is a WOT box install (No-Lift Shift, 2-Step, which if you're considering I highly recommend as it was the best $200 I've ever spent). I followed the directions to a T, making sure every wire went to it's directed source. The WOT box basically takes control of the Throttle Position Sensor, Crankshaft Position Sensor ,Cruise Control Clutch Switch (Clutch Deactivation Switch) and Ignition Coil Power wires that are connected to the PCM's and ECU. The thing works flawlessly so I know I don't have any loose ends or undesired wire connections.

So I figured I would recharge the whole system as I know there's a pressure sensor in the A/C compressor that only engages if it's to a certain level. So Brake Masters took care of that for me, and didn't charge me as it was done less than a year ago, but they said it was an electrical issue I was facing as the compressor is not kicking on. They claimed they checked fuses, but I wanted to be sure, so I checked the specific fuses for the A/C Compressor which are 25 10A** A/C compressor relay and 43 G8VA relay A/C compressor relay in the owner's manual. The fuse was fine and the relay is questionable. I came to the conclusion that if I run a jumper wire from one end of the relay to the other, the compressor's clutch engages, and BOOM! The A/C is as cold as could be. So I said it's the relay! Which are like $35 from the dealership, and I found one on Ebay for $10, so I ordered, waited a few days and tried the new relay today, no dice. So I swapped my other relay for the Fuel pump (41) thinking I just got a cheap relay, but that didn't work either. So either my relay for my Fuel pump and this brand new relay is faulty, or I have some other sort of electrical issue. I cannot figure it out and really need some help before temps hit 115 out here.

Here's the red wire I've been running to let the compressor clutch engage.
 

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Maybe the AC Pressure switch is bad? Perhaps pull the wire off and short the pins on the wire? Some pressure switches screw onto a Schraeder valve and don't even lose pressure when you change them. If it is the pressure switch, hopefully it is that kind.
 
Turned out to be the high pressure sensor switch which I was unable to locate on my own, the harness had melted and was telling the ECU a constant extremely high pressure due to it grounding out. A local mustang swap changed out the switch, harness and evapped and recharged my whole system for around $400 and the issue has been completely resolved since.