1998 Ford Crown Vic - HVAC Problem

[crownvic]

It has heat on the floor & vent.If you put it to defrost it will turn to a/c.

[Rich]

In the defrost mode the ac compressor will come on and also indicate that on the controller.

Does this have ATC or is it manual?

[steven kiser]

defrost will always turn a/c compressor on. check for vac leaks. i've seen the vac hose off the vac plug and it kinked where the heater box mounts to the firewall. coffee or soda spilled into vents will jamb up vent doors. i would check to see if a pencil or other implement has fallen into housing. am trying to recall if the door is vac or electric. elec I'm thinking. the motor can be accessed and replaced without dropping the box. as a rule if there is a big brown stain on the motor i've found door to be difficult to move causing it to overheat and burn up. if heater box has to be remover remember to include a/c service and heater core replacement. good luck..........................

[crownvic]

I know the compressor turns on in def mode,but something is making the accuator go back to cold mode only in def..If i put it back to the floor mode it will get hot again,that tells me the accuator is working.Is there a module that controlls that?

[ricmorin]

We're gonna need to know if this car has ATC or a manual system.

[steven kiser]

just for s and g's before we get into blend door issues and such lets get back to basics. when the car is fully warmed up grab the heater hoses at the core. if you can hold them chances are the core is restricted or someone got a bit out of control with silicone sealer and the port on the intake is plugged. for some reason on my first post i completely overlooked the fact that at least with my experience the core is restricted enough to allow the a/c to override it's heating ability. some shops will disconnect the a/c compressor and call it fixed. as a rule (with fords) if the heating system is functioning properly the heat coming out of the vents (nearest the core) should feel like the heat from a hair dryer. another issue overlooked at times is the t/stat. i will let the car idle at approx. 3k and watch the gauge. after it reaches and maintains operation temperature I'll place a high volume an in front of the car and blow air through the condenser and radiator. I'll watch the temperature through the scanner. i never rely on the sensor readings when I'm trouble shooting. i will use an infrared gun to compare the temperature readings as well. repeating what i said about holding he hoses, f you grab them and have to think about if they're warm enough they're not. they should be so hot they sting. if you grab them and pull your hand away and get mad that i suggested this then the flow is good. it should be within a few degrees between the to hoses. if you have to replace the heater core have a blast. they're not as bad as a taurus but pretty close........................................

[crownvic]

There is no restriction both hoses are extreamly hot.It seems like when i switch modes to defrost somthing is telling the blend door actuator to switch to a/c mode,soon as i put it back to the floor to acuator will switch back to heat mode.

[crownvic]

It has atc.

[ricmorin]

OK. There is a module that controls this. The EATC module (control head) controls the blend door actuator on this. It is electric. Check to see if the blend door is broken. It and the actuator are located on top of the heater box I think. The last one I could see by removing the glovebox and looking in there. Either the air volume is forcing a broken door over or the module is erroneously commanding the door. A visual inspection and a voltmeter should tell you. BTW, any codes in there?

[steven kiser]

defrost will call for the a/c compressor to activate. there is a temp. sensor that will mess up (especially if the customer has a dog) causing a blend issue. I've popped the sensors out and seen them all plugged up with debris. like ric said the blend door motor may be no good. it can be replaced without dropping the heater box by unbolting the mounting plate then removing the sensor from it. patience and small hands with long fingers are a plus. I'd look towards the sensor and the fan attached to it.