robkelley13

Have an '02 F-150 Lariat with the 5.4. My AC cycles from the vents to the defrost and back on its own. Could it be low on freon or is it deeper than that? What are your thoughts.

Jktx21

My 2002 King Ranch does the same thing. I just posted about this in another thread. It seems to happen when I first start the truck and when AC is set to max. Will start on defrost and then cycle to vents for a while until, then seems to stay on vents. My guess its probably a faulty mode mix actuator in the dash. I don't think low refrigerant is causing this type of issue.

robkelley13

Mine is doing it consistantly, it does not stay either. Gets kind of warm when it is on defrost. I was just wondering if it was freezing up due to low coolant and the defrost mode was a way to dethaw. Sorry for the double post, did a search and nothing came up useful.

Jktx21

My AC "freezes" up on occasion. Normally happens when I have been driving for 45 minutes plus, on max cold, the blower set to low / mid low. I can resovle it by cycling the temperature and the mode (floor, vent, defrost, etc). I think the dash and vents get cold causing the actuators to stick, not sure?

I know for a fact my AC isn't low on refrigerant, as it was just checked last week.

udderbrudder

If the heater control loses vacuum, it's supposed to revert to the def. setting for safety reasons (you can drive with cold feet but not with a fogged windshielld). I'd start by checking the vacuum supply to the heater cont.-check the hose which goes thru the firewall to the heat cont. If it's OK - check all other vacuum hoses and vacuum motors for leaks.

vgavagan

I had a similar issue. In my case, it was vacuum. I had a bad check valve. When accelerating, I'd lose vacuum and it would switch between air vents and defogger.

By the way, anybody know of a good source for all those vacuum lines and hoses?

robkelley13

Dealership is telling me it is the AC Automatic Head Unit. It will be $970 to fix. The head unit alone is $800.

Anyone else have this problem?