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Old 06-12-2021, 08:00 AM   #1
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Dash A/C question - didn't want to hijack a thread

I've recently heard something several times in the last month that I've not heard before, or didn't listen when it was spoke of.

Our dash air, like a lot of others it seems, is not the coldest at times. I always chalked it up to trying to cool the front vs fighting all of the heat in the rest of the coach.

What I've heard is to "turn off" the hot water line coming to the dash air and this could/should improve things. I have no idea where this line is and how I would turn it off unless it literally has a valve. Would like to try this on our coach to see if it has an impact so anyone who can lead me to the hose, valve, and or a method to turn it off, would be appreciate.

And just in case anyone is wondering, I do realize we can only expect so much going down the highway if we don't turn on the genny and roof ac's, which we do a lot of times.
Scott and Deanna Brandstetter
2014 Tiffin Allegro Bus 45LP
Domicile and current home, Jacksonville, FL
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Old 06-12-2021, 08:27 AM   #2
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You can use a valve like this one: that closes the coolant loop with vacuum. I am not endorsing that specific one, just using it as an example. They also have manual cable operated and electrically operated versions. You’d want to find the right size for your system and ideally one that connects to both sides of the coolant loop, so it sends the flow back on the return side instead of just closing the supply side.
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Old 06-12-2021, 09:03 AM   #3
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Not sure if Tiffin installed any extra valves. On Newmar they sometimes installed them back at the engine on drivers side.

Your heater hose up front most likely on are passenger side.

What I would do is after taking a drive with heater off.
Pull the hood and go feel the hoses if the existing heater control valve is working correctly both heater hoses will be cold.
If this is the case then your lack of cooling is not from a failed heater control valve. These were installed backwards in some coaches causing failures of the valve and hot water flowing through heater core all the time.
2002 Newmar Mountain Aire 4095
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Old 06-12-2021, 10:05 AM   #4
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There are two hoses from engine block to heater core. They make ball valves with two hose barbs built on even in 5/8 hose barb. One valve would test the theory ,two could save a trip or from getting stranded if those 60 plus feet of hose would fail.
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Old 06-12-2021, 12:53 PM   #5
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Just feel the two heater hoses up under the front if one is warm and the other cold your valve is shutting off. If one is hot and the other even slightly warm your valve is leaking. You can replace it or add a manually controlled one. Some heaters do just have the flapper close off the heater air. If the flapper seals fail you will be easier off to just add the valve. An ac cannot even begin to overcome the heater if it's getting hot water.
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Old 06-12-2021, 03:47 PM   #6
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Scott, you're talking about the heater control valve. When you turn on the dash heat, the valve opens up and circulates hot water through the small heater core under your dash. Your dash fan then blows past that heater core, heating the front of the coach. The issue some have, is that heater control valve gets stuck in the OPEN position and allows hot water to circulate all the time, competing with the air conditioning.

You can check it, in the manner mentioned above. It's a metal valve, with the two heater hoses attached, one in and one out. However, I doubt that your year coach is having that issue. It would also compromise your A/C all the time, not just now and then.

Many of the builders place valves next to the driver's side of the engine (hoses running parallel to the engine block). Mine have yellow handles. You should know where these are, in case you ever burst a heater hose that runs the length of the coach. You can close the valves and still drive the coach.

Back to your don't say if it cools normally at any point and then stops, or starts and stops. My current coach would cool well and then suddenly, poor cooling. A while later, it would cool well again. Mine was a cold control switch under the front hood on the condenser box. It was telling the unit that the condenser was freezing up and shut down the compressor.

If yours is running cold and then warm and cold again, you need to to take it to an expert and let them check the various components.

This is a handy tool to have (Available on Amazon for a few dollars) to stick in your dash vent, nearest you and watch the temps as you drive.
Don & Mary
2019 Newmar Dutch Star 4018 (Freightliner)
2019 Ford Raptor
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