sd463d

2011 Mustang GT. Okay, so recently I noticed that my cabin air motor was blowing a little weaker than usual and just having various issues in general so I thought what the h*ll I'll just replace both the blower motor and the resistor. Car has about 100K miles on it so I got good life outta it. Got the resistor and motor from a local parts dealer. Installed both and the fan roared to life. Job well done right? Wrong. Now my compressor won't kick on. It does however start when I jump out the relay. Keep in mind that I did in fact check multiple times before my little operation that the compressor was working great. So...what happened here? Compressor works fine before resistor swap. Compressor starts right up when relay is jumped out. My thought at the moment is that I did not get the correct resistor for my car from the parts dealer. I wanted to hear your guys thoughts before I plunk down about $130 at my local dealer for an FordMoCo resistor (so I'm sure the part is correct). I was an idiot and tossed the old resistor thinking my job was a success. Thanks and any and all input appreciated!

**Edit: I also already tried a new relay from Ford. I also was able to measure ZERO current going into the relay under load so I'd not getting the 12V needed to pull the coil. Problem is before the relay based on what I've seen.

houtex

Checked the high and low pressures? Checked the pressure sensor?

The resistor and blower motor are completely unrelated to the compressor (with the exception being the HVAC system turns it on and off, but other than that) so it's a simple coincidence, nothing more, that the compressor's unhappy. Or more to the point, the system that turns the compressor on/off is unhappy. Which is usually related to the pressures being wrong (too much or too little) and/or the pressure sensor being upset/dead/wrong/? With maybe the wiring thereto, and/or the SJB/climate controls being unhappy.

My bet is the pressure sensor or there's low coolant in the system, but that's at best a guess. Here's the manual for diagnosing the entire thing: http://iihs.net/fsm/?d=975

Hope that helps, and welcome to the forums!

sd463d

So are the high and low pressure switches before the relay? Sorry, I'm **** at reading schematics.

houtex

The pressure switch... well, to be sure, it's a transducer... is independent of the relay. The relay is told what to do by the PCM. Here:

The HVAC system start page:
http://iihs.net/fsm/?d=711&f=055%20-...l%20System.pdf

The Transducer:
http://iihs.net/fsm/?d=711&f=055%20-...System.pdf&p=5

The clutch overview:
http://iihs.net/fsm/?d=711&f=055%20-...System.pdf&p=6

Now, if you go through all that, you'll see that the controls in the car talk to the rest of the car through the SJB and then to the PCM. The Powertrain Control Module (aka the Electronic Engine Control) is what actuates the clutch. The PCM gets pressure information from the transducer, as you see in page 5. The PCM then turns on or off the clutch as needed. The reason it controls the clutch is because it can also turn it off at wide open throttle or other conditions the computer's programmed with... such as the evaporator core freezing over. It'll turn the clutch off to prevent that. Or the pressure transducer's indicating high/low/incorrect information.

This is where the transducer lives:
http://iihs.net/fsm/?d=982&f=Air%20C...20View.pdf&p=4
It's attached to the output of the compressor, going right to the condenser. You should be able to see it on the right side of the bay, 'under' the BEC.

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Now, with all that said... this is getting into maybes and possiblys. You might want to consider getting a hold of or going to someone who has a scantool that'll talk to the car and tell you what's wrong. The car does know. Let it guide you, and don't fire a parts/time/money cannon at it, that's my advice. For what my opinion is on it anyway. You do you.