[AL]

Based on my fan / blower issue I had to replace my dash a/c control unit. At the back of the dash control the sensor plugs in. Wiring runs upward behind main dash. I found my sensor in one of 2 wiring looms underneath and laid next to a metal brace. Its beyond me how Prevost just wrapped this up never to expose the sensor to the open air surroundings to take temp. reading. The sensor is at the end of a wire and about the size petit size green pea.

It has been pretty common for Prevost saying there is no control adjustment of dash temp. Wide open heat or full max cold.

After finding my sensor buried… I can see why and it all makes sense.

If you have no blower issues my advice is to go after the sensor and simply move it where it could pick up the temperature. Put the dash back together to give it a try. Sensor wiring is the small triple plug on dash control box

If the sensor is bad meaning no change took place in your trial, let me know. I have saved my old sensor which seamed to be working when replaced with the upgraded dash control, and new larger sensor which by the way has now been relocated above drivers right knee.

On this thread take a look at my post dated 1/15/2016. Back end of control is pictured along with new sensor update.

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Thanks Al, that might be my problem.

Thinking some more … doesn’t the converter build the dash? Wouldn’t the converter put all the wiring together behind the dash?

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Here is your ac / heat sensor that most have buried behind the dash. Yes, it is at the end of line and appox 1/4 ” X 1/4 ”

NOT the rectangle piece but half of rectangle piece. Good luck, if that can regulate minor temp change buried in a wire loom.

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Thanks for info. A little more on my problem. Heat will not turn off so I turned off water valve to front of bus and now air cond works because no heat coming forward. I can operate like this for a while and next time at Prevost let them check for problem. Thanks again

[Thad]

Al – Dan has dash air not OTR and different control.

Dano – I would bet money it’s the blend switch not shutting off the coolant. Had the exact same thing on my 97 Marathon and that was the culprit. It functions just like your car, adding or closing off the coolant loop as needed to maintain the temperature. Easy fix, it’s mounted up high behind the front bumper.

[Chris]

Tom was that “blend switch” on an H or XL?

Does the “blend switch” work an air damper? Or a valve in the coolant plumbing?

[joel]

Elecric valve in the heater hose that controls the amount of coolant to the heater core.

solenoid valve designed for smooth closing is

used to control the coolant flow through the

driver’s heating unit. The valve is made of

forged brass with internal brass or stainless steel

parts. It is mounted on the coolant inlet line of

the driver’s heating unit, and is accessible

through the spare wheel compartment (Fig. 41).

The valve cannot be manually bypassed.

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1999 XLV X-6872,  liberty #440

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On my 1989 chassis, this valve was serviced by a power wire with an in-line plastic screw type fuse holder. Fuse holder broke=no power to valve=full eat on.

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Do these have a tendency to stick partially open/closed?

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If anything the seat fails and they fail to stop the flow.

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Jon wrote: “If anything the seat fails and they fail to stop the flow.”

Which could inhibit the effectiveness of the OTR A/C?

What happens when I flip the switch on the OTR to A/C? Is this the only device that stops the flow of coolant to the front of the coach? Or is there another valve in the back of the coach which shuts the water off back there?

Confirm for me that the rheostat on the dash controls the coil on the valve you pictured to variably open and close the water valve. Essentially if this works correctly, the valve isn’t just a simple fully open or fully closed valve.

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If I remember right the thermostat uses coolant to modulate the AC temp. So as it gets a little chilly the valve opens sending a little warm coolant through the heat exchanger that warms the flow of air through the AC evaporator.

I think.

When in heating mode this is regulating the flow of coolant to control the temps when they get too warm. The fan is a constant in both cases.