I have a 99 F250 Diesel truck and I am having a problem with the air conditioning. It will blow out somewhat cool air when you put in on max a/c for a little while then it will start to blow out warm air, but sometimes it will start to blow out cool air again. I took it to an ac repair place to have it charged and they said that it was fully charged and they couldn't put anymore in. I would like to have somewhat of an idea what could be going wrong before I take it in.

Also, I don't know if it is worth mentioning that the wipers don't work all the time either. It doesn't matter what setting you put the switch on, they have a mind of their own as to what speed they operate at. This truck has 206,000 miles on it.

Thanks

 

ukcolin,
I'd try a different A/C repair facility! Did they even measure the air temperature at the vents?

Without knowing anything about your system like the pressure readings......my best guess is that your A/C is slightly undercharged and the evaporator is freezing up. When it freezes, the evap can no longer absorb heat from the cabin and the air coming out of the vents starts to feel warmer. After a while, the A/C cycles off, the evap thaws and the air feels cool again until the whole process repeats itself.

Again, this is just a guess.....without knowing pressures and temperatures it's impossible to actually determine what's happening.
The main thing is that you need to find a A/C repair shop you can trust. I hope it didn’t cost you too much to tell you the A/C is fully charged. Find another shop!

I doubt the windshield wipers are related to you’re A/C problem……
Phil

 

you could try the touch-feel test. locate the lines going to the evaporator and feel them. the evap is the part inside where the absorption of heat (A/C's don't make cold...just less heat!) occurs. the inlet (smaller tube) should be cold to the touch...the outlet tube will also be cold (about the same temp as the inlet) if the refrigerant system is fully charged and functioning properly. the condenser is the part in front of the radiator and the lines to it will be hot and really hot if everything is working correctly...be careful.

short of installing pressure guages...this is about all you can do...and the purpose of doing it is that it's a quick way to verify that the refrigerant system is working...so...if a vehicle is blowing hot air AND the refrigerant system is working, then there is an air delivery problem inside the vehicle...and adding more juice won't help, in fact, it may cause the compressor to fail.

 

If in fact your system is fully charged then you may have a problem with your compressor clutch. Not sure exactly which compressor is used on your truck but typically after a couple hundred thousand miles the clutch air gap can widen a bit and then the magnetic clutch sometimes will not engage causing symptons that would be similar to what you describe. Another item that can affect clutch engagement is the low pressure cutout cycling switch. If I were you I would be doing a couple of tests to determine the problem. First go buy yourself a set of R134a manifold guages hook these to the system and get some baseline readings and record them. Do the test readings with the AC set to Max blower on high speed doors open and windows down be sure to record outside ambient air temp in front of the condensor also. Next get out your set of feeler guages and check the compressor clutch air gap it should be around 25 thousands. If gap looks OK then observe operation of the system set the blower its lowest setting with the system set to max the compressor with the doors closed and windows up truck in the shade you should get the compressor to cycle on and off under these conditions watch for periods ot time when the compressor disengages on low pressure (around 20 to 25 psig on your low side guage) then when the pressure equalizes back to above 50 to 55 psig the compressor does not kick back on. Now if you catch it where it is not kicking back on as it should take a hammer or screwdriver and lightly tap the front of the compressor clutch if it immediatley engages adjust the gap tighter (if that does not work replace the clutch) if it will not kick in with a tap then replace the low pressure cycling switch. Stay cool man. Key is to have a set of guages hooked to the vehicle so you can see what is going on inside without it you are a blind man walking thru a minefield

 

I think I would buy a new A/C relay for about $ 15 and swap it out with the old one. Then if that one is ok, change the other (fuel pump relay) I know this has nothing to do with it, but every time I had a problem on one of my Ford trucks. It was a switch or relay. My electronic trans stopped shifting on a 2002 Ranger because of a burnt out turn signal. There is a common fuse at the flasher and trans. My Battery would not charge on my 95 f250 because the A/C relay was stuck and bled the juice out. I doesn't make sense, but the reason I know that was the problem, is that when the relay was changed, the problem quit. Same with the tail light bulb. I always carry spare fuses, bulbs and a relay with me.
Good luck