Air Conditioning Failure


Yesterday while I was out driving the air conditioning on my 1999 Mercury Grand Marquis suddenly started emitting hot air instead of cold/cool air!

What is the likely cause of this? Does it simply need recharging or might it be an electronic problem?

Should I go to the dealership or will an independent mechanic be able to deal with it?




Air conditioning is a bread and butter repair at most auto repair shops. It might be something simple like a blown hose or seal. A dealer repair is not needed…Ask if the shop has an ASE certified air conditioning tech and if so, you should be OK…


Is this electronic controls (EATC) or does a dial with blue/red control the temp? There is a self-test procedure for EATC, but I don’t know it. Someone at www.crownvic will know. You need to see if your compressor is engaged when the AC is tuned on. Open the hood and see if the compressor clutch is operating. If it is, and you have manual controls the blend door is probably broken. If that is the case, you can bypass the heater core for the rest of the summer.


It sounds like you’re saying it just suddenly went from refrigerator to convection oven. A loss of cooling that instantaneous has to be a compressor clutch or control failure, or possibly an HVAC programmer problem (if this vehicle has digital control.) Or in other words, this is unlikely to be a leak. I’ve never seen it happen but a failure that rapid caused by a leak would probably have made a loud WOOSH sound and possibly created a cloud of gas. Lol.

The first thing to do is determine if the compressor is turning. I’m betting that it isn’t. Start the engine and engage the A/C, set the temperature controls to maxmimum cooling and open all the windows. Open the hood and look at the air conditioning compressor. The entire pully (both the outer portion and the center face) should be turning. If it is not, then you have an electrical problem such as a switch or relay, or possibly a leak has caused the problem. If you have some experience with electric circuits, and have a voltmeter handy, then you can track the compressor clutch circuit from the compressor harness back to the relay, until you find voltage. If you find voltage present at the compressor, then you have a failed compressor clutch which will have to be replaced. This repair is best left to a shop, as is the diagnostic proceedure if you don’t know what you’re doing.

If the compressor IS turning, then there’s a chance that the blend air door has gotten stuck in the HEAT position somehow. To check, get back in the car. Switch out of MAX A/C and into normal. Hold your hand in front of the vents as you disengage the A/C (if you have digital control, you may have to have an assistant remove the compressor clutch relay to accomplish this without changing the temp. setting) and feel the temperature of the air. Give it a good 60 seconds if necessary. If the air gets hotter, the door is stuck open in the heat position.



Catching a stone in the condenser can cause a sudden loss of pressure. It might be unusual, but it happened to me once.