I have an 1999 f 150 that is blowing cold air I believe it is stuck on the a/c mode and when I put the heat mode on it is still blowing cold a/c.It has been doing this the last 2 winters ,but this time it will not change over as it has before//is there a solenoid or a sensor in the a/c ..heating that need s replaaced??

 

First, check the basics. If you have manual temperature control, try pulling each **** off the faceplate and checking behind to see if any **** connectors (half moon type) are broken or split.
Listen for the AC compressor actually clicking on/off in the engine compartment with the mode selector in Defrost/AC/Max AC positions. (In my experience, the full heat from the heater core more than makes up for the AC system cold, unless engine temp is low because of a stuck open therostat...) If AC cycles off and on about 15 to 45 seconds apart(depends 'alot' on ambient temp), then AC is functioning normally. You may have either a bad blend door motor or a broken blend door, each of which determines the mix of cold air vs. hot air through a "blend door". The blend motor is a fairly cheap fix. If it is the blend door itself, it becomes rather expensive as whoever fixes it will need to R&R the dashboard.

If you have automatic temp control(eatc), repost here and I'll give you a few other ideas. It would be good to know if you hear any noises from under the dash when the temperature **** is turned or if the temp through the vents changes with the engine temp.

 

Thanks for the advice.I have the manual *****,i have taken them off ,everything looks fine.I also tried the testing of the ac motor and it does click on and off.The trucks temp.is great,when I turn the selector to warm the ac motor does shut off.I took the cover off on the floor to where the floor heat comes out ,there are a few wire/connections,maybe blower assembly.I banged on it a few times and now the heat is working..

Maybe something broken to where it switches from cold/hot???

Thanks,for any more advice... Tim

P.S.I will leave the **** in the warm position now!!