Dash A/C Blowing HOT air after engine is hot

[Billy54]

2002 Holiday Rambler Class A - Workhorse 20,000 miles.
DASH A/C BLOWS HOT AIR AFTER ENGINE WARMS UP.

So far I bypassed the heater hoses with valves.
Replaced : New AC Delco compressor, expansion valve, expansion drier and 2 new switches which were hard to find since the compressor switch is out of production,but my Chevy dealer found one at a warehouse for me.
I evacuated the system, check for leaks with machine (I have a shop) and we charged it with 2.75 lbs of freon. It worked great - a/c was ice cold. Week later went on a trip - and after 3 hours of driving turned on the a/c to see if it was cold - it blew HOT AIR and never got even cool. Got home, After we unpacked I waited about 3 hours and tried it - now the engine is cold and the A/C blew Ice Cold. Don't get it- why would it blow hot air only when the engine is hot and the heater hoses are bypassed with a valve - and blows cold when the motor is cold?? Can these bypass valves go bad? I used them all the time and never had one go bad on me. I am thinking of taking off the bypass valves and just making a loop with the heater hoses. Also above the heater hoses was a switch - I disconnected it to see if maybe that was causing the hot water to flow past the bypass valve if that is possible.... We are going away again in 2 week and could use the A/C.. Any ideas? Also is 2.75 lbs enough?? I called Monaco and one tech said 2.75 and another said 4 lbs/ Workhorse said that it has nothing to do with them. There is no label that has this info on it on the parts. It is a frigette.

[C350amg]

You certainly have a leak in the system because mine even with the engine not running will open and close a few times before it uses all the vaccum in the reserve.

[glamisorbust]

AAPAK in phoenix, AZ has all the oddball A/C parts that are impossible to find. They also make new hoses to order while you wait(2 hours). This place is awesome, next time I need anything A/C I will be using them. I wonder if they sell 12v vacuum pumps, my '94 P-30 still has the vacuum loss on even smaller hills, resulting in the air dumping to the defroster. No good.

[C350amg]

P30 back on the road the best day to check the AC. Outside temp 84F 90% humidity.

I took my refrigerator thermometer for the test. Measured temp on ac vent on the drivers side around 7 feet from the blower. Temp 60F. On the right side 56F.

Cabin temp was 75

At this time it s a complete success ( ice cold) but kind of expensive 😞

[C350amg]

We are having the same type of issues, I have a 98 P30 chassis with an Evans system.

My Chevy dealer is today finishing the installation of my new Condenser and the Trinary switch (discontinued part).

My condenser was really old and nevertheless before it leaked was able to cool the place down. By the way the condenser is also used as an engine oil cooler on my year of manufacture.
So as soon as it is out of the shop I will report the results and pics.

On the other raised topics, you can install a bypass valve (I did), but it's not doing much because I repaired all the vaccum switches so everything opens and closes on demand.

Depending on the rv manufacturer you may have to watch out for the bypass (how you install it) because in my case the antifreeze is also routed to heat the hot water heater, then the floors out back and a secondary heater with blower under the bed.

[dougrainer]

mattclark2012 wrote:
1993 Holiday Rambler Endeavor

I get antifreeze coming out of my ac ducts when the engine warms up. Also the dash ac often won't blow cold air. Pretty sure it's a problem with my heater core. I'd like to just bypass the heater core. I don't need the heater in the dash anyway. I've been told I can do that with 5/8" heater hose union and 2 hose clamps. I want to make sure I'm cutting the correct hoses though. Any advice on determining this? From my understanding the heater coil is inside the a/c housing under the hood. There are 4 hoses going into that housing. 2 are bigger, thicker hoses which I believe are the ones I would bypass. The other two are smaller and both have valves on them where it looks like you would put in freon. I'm guessing those are the a/c hoses. Any light you guys could shed on this would be appreciated. Thanks

The 2 Heater hoses will have hose clamps. The AC lines will not. Usually the Heater core is on TOP the AC evaporator. Doug

[rgatijnet1]

Without seeing the system I can only give a guess. On some of the older cars that I worked on, that had AC, it was very important to make sure that the BOX that contained the AC evaporator coil was sealed. Since the older cars had the AC box under the hood, it was subjected to all of the heat from the engine. The newer cars have the AC box under the dash, on the passenger side of the firewall.
In any case, on most RV's that I have seen, the AC box is under the hood. You will have a door on the AC box that will allow outside air to circulate inside the coach when put on vent. IF this door is leaking any air from not shutting completely, or by being loose enough not to seal, you will be drawing hot air directly from the engine compartment. This would explain why cold engine, cold air...hot engine, hot air.

[mattclark2012]

1993 Holiday Rambler Endeavor

I get antifreeze coming out of my ac ducts when the engine warms up. Also the dash ac often won't blow cold air. Pretty sure it's a problem with my heater core. I'd like to just bypass the heater core. I don't need the heater in the dash anyway. I've been told I can do that with 5/8" heater hose union and 2 hose clamps. I want to make sure I'm cutting the correct hoses though. Any advice on determining this? From my understanding the heater coil is inside the a/c housing under the hood. There are 4 hoses going into that housing. 2 are bigger, thicker hoses which I believe are the ones I would bypass. The other two are smaller and both have valves on them where it looks like you would put in freon. I'm guessing those are the a/c hoses. Any light you guys could shed on this would be appreciated. Thanks

[AJR]

I had the same problem.

My 2002 Workhorse W22 uses an ACME heater shut off valve.

ACME is out of business.

Thor sent me to this place.
ACMEAIRPARTS.COM

Expensive, but the AC now stays cold.

[glamisorbust]

Where is the best place to buy P30 a/c parts around here in surprise area? Mine needs an expansion valve, high & low pressure switch and receiver/dryer. O'reilly's had some parts but nothing matched up to what I have, at all.

[harold1946]

Most of the P series chassis have the Evans tempcon valve and is a common cause for the symptoms described.
The way to test it is to have the engine up to temperature with the heat totally off. If the hose going to the heater core is hot on the outlet side of the valve it has failed and needs replaced.
www.evans.com

[dougrainer]

http://www.evanstempcon.com/tsg_RefrigerantChargeGuide.php

Copy and paste for the amount of 134a. Not SCS Frigette, but the parameters are the same.
Do NOT install a bypass. Clamp off BOTH heater hoses to the heater core and retest with hot engine. I will bet it blows cold. The ONLY thing that will cause your problem (IF the compressor is running) is hot water leakage thru the Heater core. Doug

[dougrainer]

jerseyjim wrote:
My gasser...the a/c cuts out sometimes when climbing a hill or under certain loads. But EVERYTHING cuts out. Fan, too. It's the vacuum. The vacuum cylinder is not large enough to to do the job under some stressful conditions. So the computer, I guess, shuts the system down to give the motor what it needs.
I was told that Ford had a larger vacuum cylinder for sale...and I figured, "OK, next year I'll put that in." But..."next year" comes and goes.

Install a 12 volt vacuum pump, like the Diesels have. Much more reliable than replacing or adding an extra reservoir. Doug

[jerseyjim]

My gasser...the a/c cuts out sometimes when climbing a hill or under certain loads. But EVERYTHING cuts out. Fan, too. It's the vacuum. The vacuum cylinder is not large enough to to do the job under some stressful conditions. So the computer, I guess, shuts the system down to give the motor what it needs.
I was told that Ford had a larger vacuum cylinder for sale...and I figured, "OK, next year I'll put that in." But..."next year" comes and goes.

[havasu]

I have exactly the same problem on my 95 Newmar - I have just installed 2 ball valves on the inlet and outlet from the heater matrix. Haven't had a chance to test it yet but I too was surprised that the AC blew red hot air even with a brand new water heater valve that was fully closed.

It's a pretty simple system so where was the heat coming from if not from the water hoses? If it was just warm I would say it was from the engine compartment, but it was "full on" heater hot.