I changed my coolant today, and afterward had turned my heater on to run and while it was running, I had noticed my lines for my a/c and my canister were sweating as when my A/C is set on. I did research, and had found that the A/c runs to "DRY" the air and the heater runs to heat the air. My question is do I really need my a/c on while the heater is running? Will it affect the moisture level in the car when its 20 degrees out and the windows fogging? This is my first post, thank you guys soo much, I have read alot on this site, love my Crown Vic LX and plan on being on here alot.

There should be a heat setting on your car that does not use the A/C. Since my 2000 does not have a HIGH setting im assuming its a little dif. On mine the only setting i can use (because of a dying A/C compressor) is marked Floor.

As far as fogging goes. Yes, it will help out alot. I had a lot of fog headaches last winter without the assistance of Defrost

- Somthing ive noticed most people arent aware of, i wonder how muxh of an effect on gas milage there is when using? Somthing i would like to see tested

If you set the controls to vent and adjust the temp to hot, the compressor should not be on. Only when you have it on A/C or max air, or defrosts should the compressor be working.

On most cars, the a/c compressor will not engage if the ambient temp. is about 40 degrees F. or under.

Note that turning the controls to hot does nothing to the coolant flow.

I do not believe that your AC is on when you turn the control to hot. The AC does go on when you select defrost. True, the compressor will not engage when the temp is low due to the pressure switch, not due to some temp sensor.

Does Ford A/C work different than others?
I can't find it in my Mercury manual, but for one of my other vehicles it clearly states:
"If the outside temperature is 40F (4C) or warmer, your air conditioning compressor will automatically run to help dehumidify the air and dry the windshield."



Regardless of HOW it works, the point is that to answer the o/p question, the a/c will NOT run at 20F!

You are is correct. The manuals often do indicate that there is some sort of temp cut-off below which the AC will not operate. For the average driver that is enough, but it tends to make some thinking people that there is some sort of temp sensor that keeps the AC compressor from engaging.

I was not correcting you. I just wanted to make it very clear that there is not some temp sensor that prevents the compressor from engaging.

Can you imagine an owner manual that says that that the high pressure switch will prevent AC compressor operation when the temperature drops below about 40 F? Oh, that would be a real laugh for the dealer personnel trying to explain it.

Thank you guys for all your replys. My question was answered. It was awkward to me that the A/c was running at the time I had it selected to defrost and the heat was set to hot. I do understand that yes, when it is warmer out and especially here in Omaha Ne where we get lots of humidity it would be a good idea to "dry" the air. Luckily, for my gas gauge, I dont use the heat unless it is cooler out, and considering there is a floor or vent position that the A/C wont run in either way (hot or cold out) I can control wether the A/C kicks on with the heat or not. And also, it was confusing for me to read that it would run to dry the air cause I think the A/C would freeze up when it is very cold out. There being my question being answered even furthermore about the high pressure switch, not a temp sensor, where as it wont allow the A/C to kick on in the hot defrost setting below a certain temperature.

Thanks again.

I think some or all pre-95's might actually have a coolant control valve for the heater core.

Rangers had them pretty late, but I don't know about Panthers. I was thinking about installing a vacuum-operated valve to cut some of the heat that is added to the air flow since the blend door does not seem to be 100% efficient.

IIRC, there was a TSB for "Southern" Super Duties to do just that. Apparently people complained about poor AC and there was a kit issued to cut coolant flow to the heater core in every cooling position except max. I don't recall if that max was MAX=recirculate or MAX=most blue on the dial. I suspect it was the former and used the same vacuum circuit as the recirc door.