1993 Mercury Sable. Engine running great, Daughter says AC stopped being cold. I turned on AC, and can tell the compressor does not kick in. disconnected and jumpered the dryer wire, (friends advice) still no compressor. Checked Voltage at Dryer, no voltage. Checked AC fuse (15 Amp) and found it blown. (reason for no power at dryer???) Replaced fuse and fuse blows as soon as you turn on the ignition (with ac and heat control off and dryer unplugged). With fuse blown, Heater/AC control changes air direction according to what is selected (max, panel, floor, defrost) But the air comming out of the vents or defroster does not change temperature even when engine is up to normal temperature. Radiator fan comes on when needed to not overheat engine.
This is the LS model (fully loaded) where you change the ac and heat by selcting the numerical number on the controller, i.e 73 degrees and the heat/air act accordingly.
checked the low side ac line (quick tap on the shrader valve) and there seems like there is plenty of R12 pressure in the system. I was planning on changing it over to R134a but now I don't know. My next step is to try and electrically disconnect the compressor and see if the fuse blows, but I can't find someone with small enough hands to get between the PS pump and the compressor. Any help on that would also be appreciated!
Any ideas on why the AC fuse blows??? Could it be that climate control door?
Thanks

 

See if you can turn the compressor by hand(from underneath).if it doesn't turn its your compressor, it is more than likely your comp i do 15-20 per year due to leaking through front head seal and lock up.

 

Ok, I will try that.. But how does a bad AC compressor explain the lack of heat when ac is not on?

 

I checked to see if I can turn the compressor by hand, and it turns easily. I also found out that the 15 Amp AC fuse (#17) blows as soon as I turn the ignition to acc. I don't even turn the motor over and I can here the fuse blow as soon as I turn the key.

Any possibilities?????

 

But if someone tries to say turn the compressor pulley to see if the compressor turns...doesn't that always freewheel until the clutch engages the compressor, electrically, if the refrigerant level is adequate for the switch to know that? Or is everyone trying to turn the compresor by hand, somewhere else? Just asking.

 

electrical can be a real bear, but with careful checks and attention to details you can usually isolate the short to a specific area. First lets get the electrical schematic for your particular vehicle, a subscription to alldata may be in order or a trip to your local dealers service department. With that info in hand you can identify the outermost reaches of that particular circuit. Unplug each device and try the switch in the ACC position, when it does not blow you know that the last device you unplugged is your problem replace it and live happily ever after. A entire weekend will probably be totally wasted on this maybe two or more. Good Luck

 

This one was a BEAR! Thanks for the advice from Mr. Fixit. I subscribed to AllData and got some outstanding troubleshooting procedures. Like running the AC controller unit through a "Self Test".

The reason the Compressor was not coming on was because of the 15 amp "AC" Fuse (#17) kept blowing as soon as the key was turned to "ACC". Strange thing was that the fan would blow just fine but the ac would not come on. I initially thought it was the "Blend door actuator" causing the fuse to blow and that would entail ripping out the dash to get to it. The fuse only has three things connected to it. 1. The EATC (Electronic Automatic Temperature Control) (the head unit in the dash). 2. The Blend door actuator (mixes hot and cold air for precise temperature control) located on top of the heater core. 3. The variable blower speed controller (changes speed of blower to whatever is selected on the EATC) located under the blower behind the glove compartment.

I disconnected the head unit and the fuse still blew. leaving it disconnected I disconnected the Blend door actuator, fuse still blew. Leaving both of those disconnected, I disconnected the Variable blower speed controller and that did the trick. It is a circuit board that has a high power transistor and huge heat sink.

Dealer wanted $237.00 for a new one, got it used from the junk yard (U-pull-it) for $20.00. What a relief. Air blows super cold (Still R-12) and all is well and I didn't have to rip the dashboard.

Thanks again to all who made suggestions, Especially Mr. Fixit. I highly recommend "AllData.com" to get access to some great diagrams, schematics and troubleshooting procedures. Total cost of repair was $44.95 and my time.