My ac starts out cold and as soon as i start driving it gets hot (the **** is on cold).
Please help me figure out what is wrong?

Thanks

 

I am in need of help please

 

Does the air stop flowing out the dash vents? Does it switch to the floor or defrost? If you stop driving does the airflow return to the dash? Did this problem just start? What service was done beforehand? What model and year truck do you have?

 

Welcome to fte. Tell us a little bit about your truck so that we may better help, especially the year, as after 94, they were charged with 134 A.

 

i have a 1992 f150 I6. the ac doesnot cut off at all. its at cold then as soon as i start driving it gets hot. the ac still blows when i drive and never cuts off. it started after winter. i have done all the services myself, just regular oil and i changed the brake lines.

 

Looks to me like it is time to throw some gauges on that A/C system. That will tell the story of what is going on.

 

okay thanks

 

does it return to cold when you stop and let it idle ???

 

Wild thought..perhaps the blend door is opening when driving(for whatever reason). This would allow for heat from the heater core to seep thru and give the expression the a/c wasn't working correctly.

Best idea I would suggest is to start the truck and with the a/c running and blowing cold, actuate the temp **** selector. See if there a complete motion and you can't simply pull it open when it's in the cold range.

The blend door itself could be malfunctioning or check the housing that holds the ac part near the firewall. It will be enclosed in a black 2-piece housing. It could be separating and while driving air entering the engine bay maybe blowing the housing opening and thus allowing for hot air to come in.

 

Great idea!

 

It does not return to cold.


Thanks for all the help! i will try when i get home from school

 

If ir doesn't return to cold when stop and/or sit idle, there could be a problem with the A/C itself. After starting the truck, visually look to see if the a/c compressor clutch engages when the A/C is cycling. Drive the truck and after you notice it getting warm, stop the truck, pop the hood and look to see if the clutch is still cycling. IF the clutch isn't cycling after you have been driving, best bet is to get some gauges on it as RLA2005 stated or get it to a reputable shop so they can further diagnose the problem.

When the A/C wasn't working on my ol' '92, the shop charged me about $175 for charging, replacing 3 O-rings, and a new low pressure side switch. I thougth this wasn't to bad since it was never serviced prior to my purchasing it.

 

Another possibility, if someone has recently serviced the system, it is overcharged and icing up. Been there, done that. Now I do my own A/C service most of the time.

 

Another possibility that has not been mentioned yet is an open water control valve - the vacuum-operated valve that controls the flow of water through the heater core (IIRC it is vacuum applied to stay closed, no vacuum means valve is open).

The air first travels through the A/C evaporator coil, where it is cooled and dehumidified, before traveling through the heater core. If the heater core has hot coolant flowing through it, the cold air will be reheated. This is desirable when you are trying to defrost the window, but not so much when you want to cool down the cab.

And when the engine is cold, the heater core is cold also, so this could explain the cold air at first and then none after the engine warms up.

 

This vintage truck does not use a water flow valve for heater functionality. There is a temperature blend door in the plenum chamber. Perhaps you are on to something there but in different way.