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Don’t know about your’s but with mine (1991) every winter, have to educate myself how the back and drivers air works with the knobs on dash. Takes a minute or two to change temp when running down road. The mixing valves for heat must be slow and complicated. Are the valves opening or moving? Think they are behind front dash. On mine, just pull access cover. Don’t think i could figure out these new coaches. Take Care!

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Mike,

it sounds like you have the OTR system. On the dash, turn on heat and set temp to max and then check the circulation pump in the OTR heat exchanger bay. It should be running. If the pump is working, check the central hot water solenoid valve at the driver’s heat exchanger. Put 24V on it and it should be clicking. If both operate you still might have an air lock. If neither are operating, you have an electrical issue. Check fuses.

The maintenance manual on the Prevost site has a good section on how to check operation of the heating system (Chapter 22).

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Thanks Glens and Threegreens, My 91 heat has not had to be used for about three years due to mechanical motor issues. Finally getting her up and going. I had to replace batteries last week and in the process found two wires not connected. The first time I tried the heat I checked the heat exchanger bay and it seemed like the pump was not pumping. I went back to the batteries and connected the two wires and now I can feel vibration at the pump. Will check the solenoids today. Found two solenoids in the spare tire compartment that go up to the dash coils from the heat exchanger. Where can I get chapter 22? Thanks! – Mike

[John]

go to prevostcar.com web site use last letter in your serial # and last 4 numbers technical publications prob maintance manual is what your looking for under heating and aiconditioning. You can download complete book specfic to your coach. for example last letter Mine W= year built last 4 numbers 6553= unit number. Hope this helps Bob

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Thanks Bob, Found it. Hows your weather? Today we got Rain and 67 ….. I’ll take it!

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should be large (1 1/2 in line) elect valve in side compartment where pump is also.. ck it. don’t buy –I have one I don’t need. Bob

[Bob]

Rob, Ok, I will let you know if I need it ….. Thanks!

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I’d be interested in a diagram on all of this if anyone has it, or at least some guidance. I have no idea about where to look for a heat exhanger bay or anything. I was told there was a big valve near the engine. Found that. Still nothing but cold air at the dash. Guidance would be appreciated. I tried to find something at the prevostcar.com site and was told No Results. Thanks.

[Archived]

Dale,

One problem with any of us trying to advise why you have an issue is the Prevost cooling system which is also a part of the OTR and driver’s air system is that the system might be modified by the converter.

So all of us need to first identify all the valves that could be scattered through the coach that might be closed, and get them open. If the coach has a Webasto (not an Aqua-Hot) it is likely it has been set up to run in parallel with the coach coolant system, but it could just as easily been set up to run in series making valves in that system capable of controlling coolant flow to the OTR and driver’s air heat exhangers.

So regardless of whether you have OTR or just driver’s air the only thing I can suggest is to start at the engine and open every coolant system valve you can find including those that might be hidden, such as next to the radiator behind the radiator door covered by a flap. If you have OTR look in that bay. Go to the Prevost Car site, access the service manual, and verify you have found the valves relating to the Prevost systems. You will have to do the same with the converter installed portion of the coolant system.

If the systems have solenoid valves one thing I would do is verify they open. I would check the coils for continuity and if that checks out I would verify they are getting power to open the valve when heat is called for. On my second coach I ended up making my own sketch of the coolant system which was very time consuming, but it did allow me to understand it better and know which valves I needed to open or close to accomplish what I wanted.

[Peter]

Long time no talk. ck inside driverside behind rad toward front for ahut off valves.. 2 each from engine to heat exchanger. Aslo on driverside in evaporator/heateer bat look for a electric selonoid line valve that shuts off flow from switch signal from front (24 volt) if memory serves me correct. Also in front tire compartment/maybe cruise air now should be anothe elect selonoid that controls flow of coolant to heater/defrosrer that is normaly closed==need power for hot coolant to get past it.(usually close to top of enty step (under) area… Air in system is e problem also and needs to be bleed from defroster /driver heat coil. Bob

[Paul]

Thanks Jon and Bob. I’ll definitely check those things out when I get back to the bus. I’m down in Texas now and the buses in GA. I spent an hour on the phone with Bruce at Vulcan yesterday. Enjoyed my chat with him and learned a lot. Glad to have a converter that is so available.

I didn’t have any luck finding manuals no schemeatics on the Prevost site. It kept saying no results found. Luckily I have all of the original manuals that came with the bus new. Not sure how detailed they are on this stuff.

[Archived]

Dale, I have never seen (or don’t remember) a Prevost schematic of the coolant / heating system. And even if there is one I suspect the converter may have modified it. But the shop manual sections that describe the heat and air are going to cover the various valves that could be closed or failing to open when you call for heat.

In the shop manual you likely can find the answer as to which valves Prevost would have installed under section 5 for the cooling system and section 22 for heat and air.