Dash AC intermittently blowing cold air, then hot

I had that problem with my Rexhall with the Evans Tempcon Electronic Control. It got to where the control would not shut off after getting hot. I solved the problem by replacing the electronic controlled valve with a cable operated valve. Have not had any problems since. It was a fairly simple conversion for me, for someone that is not mechanically inclined it may be very difficult as the control panel must be modified or a cable control panel be purchased. JMO

Replace the valve.

Had pretty good luck with these guys.

Thermotion

BTPO1 wrote:
I had that problem with my Rexhall with the Evans Tempcon Electronic Control. It got to where the control would not shut off after getting hot. I solved the problem by replacing the electronic controlled valve with a cable operated valve. Have not had any problems since. It was a fairly simple conversion for me, for someone that is not mechanically inclined it may be very difficult as the control panel must be modified or a cable control panel be purchased. JMO

It is not the Valve here is what I did.

I guess it must be a Vacuum leak I put a temp shutoff valve and tested the electronic one. It is opening and closing like it should when I change the temperature control. When hot is selected valve is open, When mid point is selected it is half way open, when in the cold position it is closed. So the Evans coolant valve is working. I had the same problem using the temp shut off valve that I installed. Got to be a vacuum leak or else the door flapper is not working. The sight glass is running clear and no bubbles so I don't think it is low on freon.There is a vacuum pot on the bottom of the AC case which I think is the flapper door actuater. I could not get any vacuum out of the line that is attached but when I remove it and put it back on I can hear a sound like something is moving. I will start tracing lines tomorrow. And check to be sure the compressor is running. Hope I dont have to tear into the dash. Someone in another thread said the they vacuum pot is located by the brake system and is part of it. I am trying to do the easy things first. tearing into the dash control will be a bearcat as the whole center section bezel has to be removed. Cant get under it to access the AC / Heater control panel.
Mel

If you have access to a hand vacuum pump it would be handy to check the vacuum doors. I have seen the diaphragms go bad before. Another thought is that if there is a vacuum leak most systems default to the windshield defrost position for safety.

Yes it does sound like the valve is not the problem. In my case the valve would close off completely when it was cold, but as soon as the coolant warmed up some it would close but stay slightly open. It was enough to allow hot water to flow through and give hot air flow.

Hope when you find your problem you will let us know what you found.

BTPO1 wrote:
If you have access to a hand vacuum pump it would be handy to check the vacuum doors. I have seen the diaphragms go bad before. Another thought is that if there is a vacuum leak most systems default to the windshield defrost position for safety.

Yes it does sound like the valve is not the problem. In my case the valve would close off completely when it was cold, but as soon as the coolant warmed up some it would close but stay slightly open. It was enough to allow hot water to flow through and give hot air flow.

Hope when you find your problem you will let us know what you found.

I will see about getting a hand Vacuum pump. I am sure it is a Vacuum leak because this morning I checked the compressor and the clutch is working. I had the curtains drawn for the windshield and after checking the Compressor I noticed the curtains were moving above the defroster vents, So now I have to assume there is a Vacuum leak somewhere. Hope I don't have to tear into the dash. If I remove the doghouse I may have enough room to get into the underside of the dash by the AC / Heater controls. Got my fingers crossed.
Mel

mhbell wrote:

BTPO1 wrote:
I had that problem with my Rexhall with the Evans Tempcon Electronic Control. It got to where the control would not shut off after getting hot. I solved the problem by replacing the electronic controlled valve with a cable operated valve. Have not had any problems since. It was a fairly simple conversion for me, for someone that is not mechanically inclined it may be very difficult as the control panel must be modified or a cable control panel be purchased. JMO

It is not the Valve here is what I did.

I guess it must be a Vacuum leak I put a temp shutoff valve and tested the electronic one. It is opening and closing like it should when I change the temperature control. When hot is selected valve is open, When mid point is selected it is half way open, when in the cold position it is closed. So the Evans coolant valve is working. I had the same problem using the temp shut off valve that I installed. Got to be a vacuum leak or else the door flapper is not working. The sight glass is running clear and no bubbles so I don't think it is low on freon.There is a vacuum pot on the bottom of the AC case which I think is the flapper door actuater. I could not get any vacuum out of the line that is attached but when I remove it and put it back on I can hear a sound like something is moving. I will start tracing lines tomorrow. And check to be sure the compressor is running. Hope I dont have to tear into the dash. Someone in another thread said the they vacuum pot is located by the brake system and is part of it. I am trying to do the easy things first. tearing into the dash control will be a bearcat as the whole center section bezel has to be removed. Cant get under it to access the AC / Heater control panel.
Mel

Mine did the same but it was still not shutting the coolant flow off. Try putting a clamp on the coolant hose and see if a/c gets cold if it does replace the valve