the a/c blows cold air in park but when i drive a trucks length it turns to all hot air

 

Welcome to FTE, Tim.

How about a bit more data. What year, model, etc. Does your truck's a/c work all day in park, and not at all in drive? A little more background info, and I think we can help.

 

the a/c blows cold air in park but when i drive a trucks length it turns to all hot air
sorry about that it is a 1997 f150 v8 it will blow cold air as long as it is in park but if i move the truck it will blow only hot air even with the controls turned off constant hot air blows out of the vents

 

Its possible that the vacuum actuator is slowly going out and when you go to drive you lose just enough vacuum to close the cold door on your hvac and it defaults to warm. also open the hood when the air starts blowing warm and see if the compressor still is cycling.

 

vacuum controls the defrost, panel or floor controls. the blend door is electric (hot- cold mix). i would assume that the compressor is low on freon. it is probably running about 25-30 psi on the low side at idle. as soon as you give it some throttle and the compressor speeds up, the compressor suction pressure drops below 25 and the compressor low side switch kicks out. open the hood and look at the compressor stin. give it some throttle and see if it kicks out. should be able to set in the cab and do it in park also, dont have to move if it is throttle related.--- get a pressure gauge on the freon line.

 

By "hot air" are you saying high temp 'heater core' heated air or just 90 something degree ambient air temps?

If you've got 190 degree antifreeze heated air turning on quickly & then if you go "in park" again & get "a/c blows cold air" quickly again, its got to be trouble with the gate that selects and/or blends heat w/AC.

 

Busted blend door is flopping around in the dash plenum.

Major job.

Steve

 

if you want to call someone stupid you should look in the mirror d---head

 

Welcome to FTE Tim.

Steve was not calling you stupid, what is below the horzontal line in each post is the users signature. (See my signature for a case in point). In Steve's case, what is in his signature is his favorite quote. BTW, Steve is usually right on target with his advice. Good luck!

 

I could see where you could make that conclusion, Tim. But I'm sure that's not what was intended.

 

Settle down, there, Scooter.

I happen to be a Ron White fan.

You might want to grow up before you try swimming in the deep end of the pool....

Steve

 

well, im still wondering if we are talking about the AC shutting off and getting warm air, or are we talking HOT air from the heater core????

 

I am very interested because my 1999 F150, 4.6L with 133K is having a very similar problem. I just took it to the local Ford shop and they said that there was a problem with the "blend door" and it would require a dash removal at a cost of nearly $1000. WOW.

Does anybody have some advice on how to proceed?

Thanks Mark

 

the blend door takes hot air from the heater core and mixes it with cool outside air and sets the temperature inside the truck. if you move the red- blue temp **** and there is no change in temp out of the duct, then we are talking about a problem with the blend door--- is that what you have.. the door is controlled by an electric motor and variable positon.

 

Mark,

Your choices are pretty limited. You can find a shop to do it for $600-800 for a $60 part, or you can tackle it yourself.

If you choose to do it yourself, there are instructions around here somewhere.

However, before condemning the blend door, verify that your temperature **** does not have a split in it where it attaches to the control shaft. If your symptoms are the same as the OP's, then go straight to the blend door.

Steve