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Diagnosing AC troubles
On The Road AgainFebruary 1, 2012 | 4,346 views | Post a comment
My ‘05 Crown Vic (Ford) A/C is cycling from defrost to floor and blowing warm air only. I had a shade tree mechanic look at it only to say the fuses were ok and that it must be something electronic. Any thoughts?
Robert, since your car has a computer-controlled climate control, you should try resetting it first. Push and release “floor” and “off” at the same time, then “auto” within 2 seconds. It should go through a reset cycle of some kind and then blink or display a code. Then hit hot or cold to set it back to normal operation.
If a code is present, it will assist in determining what the problem is, and if not, the reset often will straighten things out for a bit. If there are no codes and it still isn’t operating properly, check for a vacuum leak between the engine and vent system.
Insufficient vacuum will make the vents default over to defrost. Having the vents go over to defrost while driving uphill, and then back to the dash vents while going downhill is almost certain to be a problem with vacuum, as the engine produces maximum vacuum coasting and nearly none going uphill. If this is the case, check to see if a plastic vacuum line has been rubbed through, if an inline one-way valve has blown out, if the vacuum reservoir is cracked, or if the control unit is malfunctioning.
The lack of cold air could be the control unit or any number of other issues causing the compressor to be stationary. A bad compressor, high- or low-pressure switch malfunction, low Freon, a thrown or broken fan belt, or misaligned blend door could all be a cause for why the compressor isn’t working. Good luck, I hope it’s something simple.
Send your vehicle maintenance questions to Jeff Deines. Email nkilbey-smith@wcn-online, putting “OTRA Question” in the subject line.
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