A/C Trouble
 

I got my Mustang out this Wednesday. It had not been driven since October. I find that my A/C is not working. It was working when I put it away. It is a whole new system. While trying to diagnois the problem, I see the pump is not turning on, the center section is not spinning. So I assume it is an electrical problem. I do not have an owners manual for this car, my 1993 Mustang SSP. I checked all the fuses under the drivers side dash. All seem to be in order. Are there any other fuses I don't know about for the A/C system? Could the selection switch for the HVAC become bad?

Toshi, my guess would be that the system has bled down from leaking seals at the line connections and or compressor seal. With low pressure in the system the compressor clutch will not engage. There is a pressure sensor switch atop the dryer canister/line on the passenger side of the firewall that prevents the clutch from activating if the pressure is too low. It's a safety switch to prevent compressor damage.

Toshi,
I agree with Greg 100%, You can put a jump wire at that switch connector and see if the system then works and gets cold ???
If it gets cold then you know it's electrical and the freon level is fine ..
If it still does not get cold i would say to update all your seals / evac / recharge.
the seals are very common on the mustangs.
hope this helps some .;)

Thanks Gregg & Hector. Yes, that helps a lot! It really does.

The whole system is new, seals and all. But I did have a leak soon after the shop installed the whole thing. Supposely they fixed it. But, maybe not!

Toshi -

Pull the harness connector off of the A/C pressure switch (you'll find it at the firewall, passenger side, on top of a black (original color) canister (silver if a replacement canister). Once you pull the connector off the switch, get a paper clip, open it, bend it to form a "U", then insert each end of the "U" into the harness connector's female sockets. Now, start the vehicle, put the air to MAX A/C and w/ the vehicle in park (or neutral w/ ebrake on for a manual), see if you can see the clutch on the A/C compressor turn on and it should be cycling (you should also hear a distinct "click" when the compressor turns on). If by jumping the switch the A/C kicks on (air is getting cold) and the compressor cycles over (clutch activates at normal intervals), then your problem is the A/C pressure switch.

To replace the switch, just twist it off of the canister (it should not be installed super tight). A new switch is around $20 +/- at any of the common Auto Parts stores and you install the new in the reverse manner. Super easy, less than a 10 minute "job".


Now - if when jumpering the A/C pressure switch connector your A/C compressor cycles sporadically, or I should say, it keeps turning on then off rather quickly, then the A/C system is low on freon. You would then have to check for leaks, because adding new freon would be waste if you can't find the source of the leak.


The A/C pressure switch is the most common point of failure within an A/C system, especially on the Mustang 5.0's (also prior F-Series and Broncos). It's a cheap part than can be easily diagnosed. Sometimes they can be bad right out of the box too.

Best of luck!

Thanks Phil. I'll give that a try.

Phil - I did as you suggested. I got the compressor to turn on. And it ran continuously. It never did cycle on/off, but I only ran it for about two minutes though. The air did not get cold. Nor did the A/C line on top of the pump get cold. Condensation usually accumulates there, here in the humid air we get in Michigan.

Maybe I have a bad pressure switch and leak at the pressure switch?

Sounds like the system is surely low on freon for whatever reasons (ie:slow leak out, etc).

If a prior shop did all of the A/C work as you said (and most is new and they recharged the system), I'd surely give them a call and ask if they can check things out. I don't know what their warranty period is for the work performed or the parts, but hopefully they would work with you in diagnosing and fixing the issue (if they are reputable and nice folks). Do you recall what the shop fixed and/or replaced?

If you had jumpered the A/C pressure switch and the air blew cold continuously, then it would have been a simple fix such as replacing the A/C switch on the canister. Now that you have jumped it and the air is not blowing cold, my guess is you definitely have a leak down somewhere which let the freon bleed off over time. The compressor should cycle (under normal operation).

Does your A/C switch on the canister look new, or does it look "old" (ie: has possible dirt around it or the connector)? It *could be* possible that the A/C switch is bad as well, like I said, they are prone to failure sometimes - but I'd rather see that your A/C system is checked for leaks before saying to replace the switch too (don't throw parts at it).



If the shop replaced quite a few components, it's quite possible maybe when they reconnected the lines, the lines were not connected 100% (spring clips loose), or maybe the O-rings on the fittings are dryrotted, cracked or misaligned - this too would cause a slow leak over time.

The shop that did the work, the whole new install and then later, the first leak check, all last summer is down by my old house, about 45 minutes away. I'm sure that they would honor their work, but it's just a pain to get down there. And then if I have to leave the car there, coordinating with someone to pick/drop me off. For the time/gas/effort, I think I'll be going to someplace closer to home.

The canister is brand new. It looked clean when I pulled the switch the other day.

Today I found out that my A/C pump is the culprit. It leaked out behind the pulley. And I think I only had a year warrenty on that pump, which would have expired June 13. I hope not.