Hi Guys, I dealt with this problem last year and couldn't figure it out. When I first start the truck (79 f150) a/c blows ice cold for as long as I don’t shut it off, went from Pittsburgh to Virginia with no issues last year. Shut the truck of and go into the store for 10 minutes and it only blows cool. I get full volume through the vents so I don't think its freezing, stuck my hand in there also and feel no ice. The system is a hybrid sort. The evaporator is 79, the comp, cond and dryer are from the donor truck, 1990 f350. Running a expansion valve from the 79 and a pressure switch from the 90. It does cycle on and off and the freeze thermostat is not wired in.
Any suggestion will help
Thanks,
Chet

 

When you say "Shut the truck of and go into the store for 10 minutes and it only blows cool", I am assuming that you mean upon restarting and not while it is turned off. My question would be when you experience the "cool" rather than "ice cold" is the compressor running or not? If the system is capable of doing "ice cold" something is providing an impediment when it is only doing "cool".

 

I had the same issue with my 02 Durango factory system. Yep first start of the day was fine till you shut it off unless off most of the day like work.
Also found if you were in town traffic stop n go, it could run warm too.

My fix was when the compressor blew up.
The shop doing the work said the evaporator was bad, crap inside it. They replaced it, compressor and the 2, front n rear, expansion valves and dryer and has been working better than when truck was new.

So if the evap was used you may want to replace it and the expansion valve maybe even the dryer.
Dave - - - -

 

Thanks for the reply.
First the comp does run when the truck runs cool. The expansion valve and dryer receiver are new. I did clean out the evaporator and cond but they are original. Compressor also is used, perhaps I,ll start with a new comp and condenser as these are a lot easier to replace then the evaporator.

 

Thing is if there is any junk in the system you are only going to push it into new parts turning them in to junk then too.
Flushing does not get it all out.
I know it hurts to have to replace it all but that is the best way to do it.
Dave - - - -

 

there are a lot of old systems out there still running well. I would ask do you have a manifold set? If not look into getting one bought or borrowed. Hook up when running cold and look, hook up again when running warmer, and log pressure differences. Do this before opening system up. I have seen farm tractors do this, it is often from too much oil, the system only holds so much, and by adding a bunch of oil, the system capacity is diminished by volume of oil. If you installed used parts, the compressor might have had oil in it, the other parts might have oil, = too much oil. A weak compressor or a weak valve could sure cause this, works ok on start up then once everything is hot, clearances go too far out. Good luck.