AC won't switch between ac and max ac their is no change in air flow all other switches work

 

It helps to know what pickup you're talking about. Sometimes the only difference between AC and MAX AC is the heater valve turns off hot coolant to the heater core. Otherwise, full cold w/ recirculate coming out of the dash vents is pretty much Max AC.

 

I have an Ex 7.3

My AC is much different between max and recirculate.

In super-hot weather the Max position is needed, at least too cool the truck off. I am in S Florida year round. Very hot and humid in the summer months.

Mine Ex has had the same problem 2x. Both times a vacuum issue controlling a blend door behind the dash.

If you have a gasser, you do not have a vacuum pump. But I guess the blend door issue is the same. Both times my issue was fixed by finding the leak. Old vacuum lines rotting. If you have a 4x4, a vacuum leak will not allow the auto 4x4 to work properly. Diesel has a vacuum pump, very much like a fish tank pump. Gassers make vacuum differently.

This problem is often diagnosed as a bad 4x4 switch in the dash. But this your last resort as you have to remove the dash. And the switch is normally not bad. If you do remove the dash, make sure to heat up the interior of the truck so your plastic clips do not break off. I would not try this at home. An experienced Ford mechanic can remove the entire dash in short order and not break anything. But you have to have done it before many times to know where to pull the dash apart without breaking anything.

If not, then check the heater valve as that is an easy and cheap fix. See post from 62 Ford250. You may not have a heater valve, depending on which truck you own.

But if your AC goes to defrost when you are commanding AC then you for sure have a vacuum issue.

If you have an Excursion 7.3 the vacuum system is slightly different than a F250.

You have a vacuum line going to the EBPV. Check that line if applicable. Both times my Ac went out this was the hard leak to diagnose.

Note: any vacuum line on the entire truck is suspect. For example, the vac line going to the auto hubs. Nothing special about the vacuum hose. Can be bought at any part store if you need some new lines.

I cannot remember but I think you can use fuel hose as well, as long as the size is the same.

Just my experience, I am not a mechanic but I am always present when my mechanic works on my Ex. Bought new and 395 k on her now. So, I have seen a lot!

 

Max AC recirculates inside air. Normal AC brings in outside air. The door that controls which air is being used must not be working properly either due to a vacuum issue or mechanical problem with the door.

 

It all depends on what the OP has. He didn't provide any details.

 

Sorry my 2008 f450 super duty single cab pickup no diesel. I had shop check Freon and pressure it’s good. But it was working at the time. But then compressor stops cycling randomly.

 

Check your compressor clutch gap for excessive wear.