Dash AC blows cold,then warm,then cold when switched to max

[Woody O]

On this trip to FL, dash AC blows cold air, then became warm air, turned AC to Max, blew cold air for maybe 30min., then began to blow warm air, switched back to regular AC, starts to blow cold again for 30min. or so. As long as I continue to switch back and forth, I have cold air.  What is defective?

Edited March 16, 2021 by Woody O
For a better explanation

[Jonbrooks]

Probably need to have service tech throw gauges on it and read the pressures to start diagnosis. 

[pennzo]

Along this same thread, (sorry, don't mean to hijack, but felt my scenario is similar) if my Dash A/C has never worked since we've owned the Coach (well, when we bought it in 12/2015, it kinda worked, but it could've been just cooler air coming in from outside 🤭) and I can't get a service appointment down here in Tampa for months, does anyone have suggestions?  Is this a DIY option or better served setting an appointment and waiting?  😣

[Ivan K]

43 minutes ago, pennzo said:

Along this same thread, (sorry, don't mean to hijack, but felt my scenario is similar) if my Dash A/C has never worked since we've owned the Coach (well, when we bought it in 12/2015, it kinda worked, but it could've been just cooler air coming in from outside 🤭) and I can't get a service appointment down here in Tampa for months, does anyone have suggestions?  Is this a DIY option or better served setting an appointment and waiting?  😣

First thing would be to see if the compressor is even turning when you turn AC on and go from there.

[powersltc]

I would try changing out the resistor.   Inexpensive.   Controls heat and air conditioning. I couldn't get heat, changed the resistor and got heat.  Haven't try A/C yet  but I think I need freon.

[Rikadoo]

Good morning everyone, having some knowelge of ac i will add my 2cents. When faced with a ac issue1st thing is to verify it is an how often it happens, the very next thing is to connect gauges an monitor pressures then set the vehicle conditions that were similar to when it failed. 
As for failure after 30 minutes my texting diagnosis will say, 1st moisture within the system, if there has been some type of recient “repair” like the system had been opened for what ever reason and either no one used a vacume pump, or had not had one on long enough. Explanation: the reciever drier is there to collect moisture by using desicant inside it, once that amount has been reached if there is one more drop that comes into the desicant it will realease one drop, that drop travels down the line to the pressure restriciting valve “either expansion type, or H type” once there the drop of moisture can actually freeze an block the flow of freon causing the system to get warm, once melted the system will resume normal operation UNTILL that repeates. I used to see that alot with truckers who had (emergency) repairs an the tech didnt vacum the system long enough.

2nd again watching the pressures when the issue develops, If while running the high side starts to climb once the pressure gets to 325psi the limit switch shuts off the compressor, THEN once the pressure returns to safe operating pressures the compressor will be allowed to cycle, then the whole system repeats the process. Explanation: Some times condencer fans when they fail just dont quit, some time just get slower an slower before they no longer function, so that would be seen by watching the high side pressures, now even if its a type that the engine fan that is used to pull air over the condencer (gas rig) then you can have a fan clutch starting to fail... again some times things just dont fail immediately.
An lastly but always a goodie a failing cycling switch, there band of operating pressures can change causing short cycling were the compressor is not allowed to build the required pressures to cool...OR what i found more often was the PLUG that connects to the pressure switch (found on ford F-650 several times) sucumbs to the vibration and the terminils where they make there connection will open an cause the compressor to just turn off untill they cool of an make another connection to turn the compressor back on...

As with anything its all about the diagnosis which makes the failure happen to ensure a quality repair.

[mike]

My coach has a similar problem with the AC. The cool air works great for about 30 minutes most of the time, then the dash fan lowers and no cold air comes out. It usually comes back to cold air after I turn the AC off for 10-20 minutes. The cycle repeats itself. I replaced the compressor last year and recharged the system. I now have colder air but the same problem. I do not have a vacuum as recommended. Could it be that I need a blower resister replacement? 
2006 Monaco Windsor 40 

[powersltc]

Ron P., 2004 Monaco Executive. 

You may need to change out your resistor.   It'll look something like this. 

Ron P.  2004 Monaco Executive. 

This is the one I used.