OTR Heat

[richard5933]

Our 4106 still has all the factory OTR heating system in place. This morning there was a nip in the air so I thought I'd give it a go and see if things work.

Well, sort of...

I know that there is hot water circulating all the way to the front since the defrost system puts out nice warm air. However, even with the temp dial (to the left of driver) all the way to 'warm' there was only vaguely warm-ish air coming from the vents.

My guess is that somehow the water modulating valve, the stat, or something else is not fully opening the water flow to the heater core.

I've got the manual and it seems to give quite a few options.

Anyone have a good place to start looking for what may be causing the heat not to flow?

Thanks
Richard

[Utahclaimjumper]

 Do you still have the booster motor and pump in place.??>>>Dan

[richard5933]

Affirmative. Still have the entire system in place. In fact, we had to use the booster pump to get an airlock out of the system when we reinstalled the generator last week.

Have both the OTR heat and a/c. Glad that they were not messed up by anyone.

Richard

[Utahclaimjumper]

 Maybe it's a Wisconsin thing??>>>D

[chessie4905]

There should be a bleed valve at top of heater core, like the defroster has. I'd start there first. When working properly, it will roast you out. If there is no air in core, use a ir heat gun to compare inlet and outlet temps at core.

[richard5933]

Heat? Wisconsin thing?

Sure is - heating season here runs about 2/3 of the year some years. I don't think the high today made it to 70. Of course, that's unusual even for us this time of year.

[windtrader]

Maybe it's a Wisconsin thing??>>>D

for sure! Nip in the air in August?

[TomC]

I removed the throttling valve and just installed a manual ball valve. I control heat by just kicking on or off the fans (2-14" 12v radiator fans). Without the throttling valve, I can get plenty of heat without the booster pump. Good Luck, TomC

[Tony LEE]

My MC8 has no booster pump and as Tom said, will drive you out of the rig if on full. My modulating valve is (pretty sure) a normally-open valve so you can easily check it by disconnecting the wires to the solenoid and then it should be on full.

I assume both gate valves are fully open back at the engine

[buswarrior]

How cold?

Idling makes little heat, but it isn't that cold yet...

No heat if you take it for a drive?

happy coaching!
buswarrior

[richard5933]

How cold?

Idling makes little heat, but it isn't that cold yet...

No heat if you take it for a drive?

happy coaching!
buswarrior

I had just driven about 40 miles. The defroster was putting out nice warm air, so I know that the system was warmed up and that coolant was reaching the front of the coach.

The air temp was in the low 50s, certainly cool enough to want to run the heat for a few minutes to take the chill off. I turned the knob on the panel to the left of the driver all the way to warm, but it did not appear to have an effect on the air temp coming from the vents.

I'll start going through the list now that I've got a few days set aside to work on it.

Richard

[Scott & Heather]

Mine was Doing this too, then I found a valve operated by a cable that opened or closed the coolant line at the front of the coach. I manually opened it and now even when it's in the teens outside, it roasts us out of the coach


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[buswarrior]

There will be a wiring issue to the regulating valve in the big pipe leading from the big heat exchanger.

GM experts, where's the valve?

The older MCI, it is up high in the front baggage bay, curb side, front wall corner beside the utility channel, behind a bent cover.

Test it with a power wire, confirm it actually operates open and closed, then go after the electrical gremlin that is obstructing. If the valve won't operate, there you go!

happy coaching!
buswarrior

[richard5933]

The 4106 has a pull cable next to the accelerator pedal, but my manual shows it controls the temp of the defrost and heat to the driver's feet. Doesn't appear to control anything other than the heater core at the very front of the bus.

The main heater core for the OTR heat is controlled by the valve in the bay just behind the right front wheel. I'll have to run through the troubleshooting list and see if I can get the valve to open. After reading the manual a few times, it seems that if I disconnect one wire the valve should open all the way and allow heat to flow at full flow. of course, I have no idea which of the many wires the manual is talking about. They all look to be about the same shade of gray at this point. Unless someone has a suggestion I'll just start pulling one by one till something happens.

Richard

[Scott & Heather]

My buses were like this ^


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