[Art]

I wired in a 24v light bulb on long wires zip tied to windshield wiper so I could see what it’s doing, (when light is on valve is closed cold) Key on fan switch on light on (Cold) turn temp knob towards warm light goes off (Hot) looking at clutch switch for AC on drawing should turn light on (Cold) but I noticed turning temp knob light is not consistent you can wiggle knob and it will change, that old switch contacts most likely dirty.

[Harry]

What do you think if I just make it simple and replace the old normally open valve with a new normally closed 24v valve and install a switch inside so when switch is on antifreeze flows and you get heat, otherwise I will have to replace the temp or even fan control

[Dave]

Art,

I was headed down the same path as you awhile ago with the opposite problem. (No Flow). I figured out during testing that the valve was fine. I had no flow because the valves on the engine coolant filter were closed. I still do not know why those valves have to be open but it definately solved my problem and that was as far as i went.

Its been awhile now but if i remember correctly you cannot us a 24vac valve on 24vdc. Something about inductive loads and heat and a bunch of other stuff i am not too proud to admit i do not understand. Perhaps one of the electrical guys can verify this. Also i seem to remember that the copper for that was 34 od heating tubing instead of 3/4 id plumbing.

Sounds like a viable work around since the dash heat does not seem to effect the overall climate in the coach very much. Off and on would be fine.i will use Jons disclaimer in that everything i said could be wrong. Just food for thought.

[Roscoeapproved]

It looks like your temp rheostat is going out. They do not last forever. On your model this should be a stand alone rheostat (vs an integrated circuit board). Should be able to get it from Prevost. I’d try to repair the original design vs. doing a “hack”.

If you can get to the rheostat, disconnect wire on one side and measure resistance as you turn the rheostat. It should respond smoothly.

---

Jeff and Lindsay

91 Marathon XL

[Ronald]

Wrong photo above in earlier post , I replaced it with the correct one above 24 DCV. And I will call Prevost and see if that rheostat is affable and how much it could be $500 plus bucks, Here is the original valve a 24 DCV valve always open, So that means if something happens to valve or electrical portion it will always be hot, If I change it it will default to closed

[Greg]

So I called Prevost and the heater temp restate is part #871076 and it is $540 bucks, So I spoke to a guy at a place that sells electric solenoids valves we talked about it and he said it did not sound like a great design to begin with,but that was 20 years ago , The electro magnet is always hot till heat heat is turned on then power is off seems backwards. So I think I will go with Plan B , I ordered a always closed 24DCV brass solenoid valve 3/4 inch it will fit right in the same spot as the always open valve and install a indicator light a switch and a fuse link and should be fine. If I want to go back to stock I can, I’m not going to do anything irreversible. All it does it let hot antifreeze flow.

[Archived]

You do realize the heater air temp will be either HOT or COLD.

When I was a youngster, we had a 1960 Mercury wagon with a broken temp valve cable. We would set it to cold in summer and hot in winter. Sucked. The people in the front seat were always too hot and we froze in the bck seat because there was no capability to circulate warm air.

BTW, I had the same problem on my 1990 Marathon but the cause was a broken in-line fuse holder in the wire which supplied power to the valve.

[Archived]

Yes I know it but we do not have over the road so besidesAqua Hot traveling down the road the dash is all we have traveling and if it is to hot I can change the switch to a simple DCVrestate, but I think without the circulation on and fan on low it will be fine?