HOT DASH AIR

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WME

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Joined
May 4, 2023
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143
Location
Riverton WY
2003 Winnebago Brave, 30 ft, Workhorse. When slow or stopped the air vents start making a lot of hot air, it takes 5 min of normal speed to cool things down. Makes no difference AC on or in vent mode. I have installed a manual cut off valve in the heater core water line.
Its been this way always, just thought I ask some new minds about it and see if there is an answer.
 
As you no doubt concluded, the HVAC-controlled shut-off of hot (radiator) water thru the heater core has failed, so you get heat all the time. At higher rpms the a/c and fans can overcome the heat to some extent, but at idle the heat dominates. The heater control valve can be replaced, but it's sometimes laborious and thus fairly high in labor cost. The manual shut-off is the less expensive solution but not perfect or convenient.

I had the heater valve replaced in my previous 2002 Dolphin LX on a Workhorse W22. It failed when the rig was only 4 years old. Cost was a bit over $200 at the time (2006!).
 
I've got the same chassis and it does the same thing. I've read that due to the limited airflow through the condenser/radiator/trans sandwich while stopped, the A/C simply can't work. I guess I could test it by pinching off the heater core hose but I wouldn't think the A/C would work sitting or underway if the heater core was hot.

Mark B.
Albuquerque, NM
 
It does it even with the manual heater valve closed. Unless there is more than 1 set of hoses, there is no hot water flowing through the heater core
 
Could be the compressor clutch is slipping - it's an easy thing to rule out. Look at the compressor clutch with the engine at idle - it should be fully engaged, i.e., spinning.
 
Check to see if the A/C condenser in front of the radiator is plugged up with dead bugs. The A/C will quit working at low speeds before the engine starts to overheat. At low speeds the engine fan pulls air through the A/C condenser and radiator but doesn't provide nearly as much airflow as driving 40 mph. So also check the radiator fan clutch to make sure it isn't failing.
 
Not the compressor, it happens when it's nice outside and the AC is off. Just using the vent mode.
 
There is no "magic" to the dash A/C system because this is an RV.

At 30 years old you need to hook up a system tester and measure the pressures and see what's going on.

At 30 years, if no done this system is ripe for a new dryer, expansion valve and maybe even a new pump.

The "test" for an A/C system is pretty simple. 1 - Is it making the pressures it is supposed to. 2 - Is the air coming out the vents around 35*F

If you don't have the tools and/or don't know how to use them at least you know the right questions to ask when you take it to a dedicated A/C shop.
 
WME said:
It does it even with the manual heater valve closed. Unless there is more than 1 set of hoses, there is no hot water flowing through the heater core
Click to expand...
The other potential source of hot air is an exterior vent door stuck open. In fact, car & RV a/c systems usually have the external vent open by default unless operating in ReCirc (aka Max) mode, re-circulating interior air. And if the a/c capacity is limited, e.g. slipping clutch or reduced condensor airflow,you may get more hot than chilled air.

Have you measured the chilled air temp as it comes out of the vents at highway speeds? It should be able to push out air at around 40 F, but RV systems often aren't quite that good. Also, when stopped, does fast idle RPMs improve cooling? Run it at 1000-1500 rpms and see.
 
The AC is not a problem it works great. When its 65 deg outside, the dash controls are in vent mode, the air flowing through the dash is cool and all is good at 10mph+. When stopped that's when the problem starts the dash air gets to 100 deg plus.
I THINK Gary might be close, the fresh air inlet is open in vent mode. Maybe what is happening when stopped is the engine radiator fan is blowing hot air all over the engine bay and the dash air is sucking it inside. Once you get moving the cooler air starts flowing in and things are good.
I was hoping that someone had this problem before and developed a fresh air snorkel kit or something to fix the problem.
Maybe that's something to do this summer.
 
Can you operate it in Max/Re-Circ mode to eliminate the vent door possibility? Assuming the HVAC control of the door actually works?

With my front engine coaches I learned to always run in Max a/c mode anyway - even in cool weather the vent air was quite warm.
 
Its been doing this as long as I've owned the RV. It's just HOT this year and finally got annoyed enough to think about fixing it.
Max-air?? kinda defeats the vent air. Maybe it will help with the problem when I'm in the AC mode, but I have to check to see if the controls are even moving the recirc flap
 
WME said:
Max-air?? kinda defeats the vent air.
Click to expand...
Yeap. But as I said, often the incoming vent air is warm or even hot unless it is wintry-cold outside.

In any case, make sure that external air intake door (blend door) is working. If it stays open on a hot day, your a/c is wasting most of its energy trying to bring the incoming air down to the temp that the interior has already achieved.
 
Gary RV_Wizard said:
Yeap. But as I said, often the incoming vent air is warm or even hot unless it is wintry-cold outside.
Click to expand...
LOL I live in Wyoming what we call a nice spring day, you probably call freeze ass cold.
Anyway tomorrow I should be able to get out to the RV and check the fresh air flap and see whats up.
I'll update then.
 
Don’t forget you have a really big heat generator radiating a LOT of heat in that little chamber under your feet, and it also contains not only the HVAC venting, but the air intake as well, sucking all the heat right back in. Engine idling, compressor not compressing (idle), bla-bla…. Even when its cool out that giant radiant metal block is really hot, and no air movement. My 85’ with a 454 did the same thing.
 
OK problem 1, the fresh air door is not closing when the control is on max air, now the search is on. Stuck door flap, bad vacuum servo, cracked vacuum line or bad controller
 
Last edited:
OK I don't know if I cured the problem, but the fresh air door is now moving. A broken rubber coupler from hose to servo
 
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