MCI Coach Heater Control Valve

DavidInWilmNC · October 21, 2007, 08:24:00 AM

My coach / OTR heater control valve isn't working on my MC-8. The green 'heat' dash light cycles on and off and the thermostat seems to control everything properly. I can hear the heater control valve clicking as 26.x volts are applied to it in response to the thermostat Both the inlet and outlet ports are hot, which indicates that the valve isn't closing. Do people repair these or is it better to just replace them? With all the converters that remove the OTR heat and A/C, I'm sure that there are a few out there headed to the scrap pile! If anybody has one that works that they're not using, I'd love to hear about it and work something out. Also, the manual indicates something about 15 volts max being sent to this coil, but I'm reading full coach DC voltage here (and the valve is labeled '24 Volts'). Am I missing something... perhaps the 15 volts is from the sensor to the controller? It doesn't look like this will be much trouble to replace, as I've got to drain the water and add proper coolant anyway, but it'd be nice to have heat that's controllable some other way than from the rear shut-off valve! Thanks!

David

Busted Knuckle · October 21, 2007, 12:02:05 PM

Agh
I was typing away at this when I lost the page! It's bad enough that I'm killing my brain try'n to think and nothing is happening! So here I am consuming large amounts of energy trying to remember the systems way of working! And if that ain't bad enough to have typed way more than this and loose it all!
OK Dave it's been way too long since I had too work on the heater valve on an MCI (what the heck am I thinking? It has not been long enough!) Ok it's been several years/beers ago! And to top it all off I've even slept since then too! But if my memory is correct the heater valve has a constant 24 volt hot wire! Then when it calls for heat (green light on) it is actually grounding the valve to complete the circuit. Which should open the valve, allowing hot water to flow and thus provide heat! Now my memory ain't as reliable as it used to be, and I've far more A/C issues lately than heat! So I may not be absolutely correct about this! But seems to me that if you'll take the little fiberglass cover off the heater valve in the right side of the front luggage bay up next to the utility channel. You should have easy access to the valve and wires, use a meter and check the wires out! OK then have someone turn the heat on while you are checking it out if the valve gets power when you hear the relay, but doesn't open/close then the valve is stuck/bad! If it doesn't have power start tracing backwards! I hope this helps, and if I'm wrong I'm sure someone will enlighten us both! LOL!

BK

DavidInWilmNC · October 21, 2007, 02:23:16 PM

Hi Bryce,

This is a normally open valve; when power is applied, it's closed. So, when the green (heat) light is on, there is no power to the valve and the water flows. When it's warm enough, the relay closes sending power to the valve and closing it. This is how it's supposed to work, anyway. Mine's always open (hot), but I can hear & feel it click when it should be closing. It may have a bad diaphragm or something. It didn't make sense to me 'til I realized that if the valve were normally closed and failed, there would be no heat at all. At least this way one can regulate it somewhat by the shutoff valves in the back.

I went back and re-read the section on the heat control system. The 15 volts mentioned is for testing purposes after a rebuild. I guess it's to make sure that the solenoid is strong enough to close.

DAvid

Sammy · October 21, 2007, 02:37:07 PM

David, test the air solenoid valve. Make sure you have an air supply to it and air passes thru it.
I just had a bad one on a DL3. Coil was "open".
Good luck.
Sammy

Dallas · October 21, 2007, 02:58:17 PM

David,

Since you said that the valve "clicks" I wonder if it's possible that you have a bad ground. The clicking of the solenoid could indicate that it's making contact and losing it again.

Gee, it's not like once a ground wire is installed at the factory that it should come loose after 20, 30, 40 or 50 years! I spend half my time trying to find the bad grounds and the other half of my time trying to remember where I layed down the wrench I was holding.

DF

DavidInWilmNC · October 21, 2007, 03:29:08 PM

Sammy, this is the water control valve. It's about the only thing that's not controlled by air.

Dallas, it's got a good ground. It's clicking when the bus interior reaches temperature; it's not a clicky-click thing like a bad relay or poor ground. It's only in response to the temp control.

Thanks!

Sammy · October 21, 2007, 05:52:45 PM

David, MCI B model and DL models have an external air solenoid to actuate the water valve.
Seems like yours uses internal water flow pressure to push on the internal diaphragm.
Sorry for any confusion it may have caused.

DavidInWilmNC · October 21, 2007, 06:01:14 PM

Quote from: Sammy on October 21, 2007, 05:52:45 PM
David, MCI B model and DL models have an external air solenoid to actuate the water valve.
Seems like yours uses internal water flow pressure to push on the internal diaphragm.
Sorry for any confusion it may have caused.

That's exactly how it works. The solenoid operates a pilot valve which allows water pressure to close the valve.

Brian Diehl · October 22, 2007, 10:36:17 AM

David, Just saw your post on the wanted section ... have you tried to rebuild the valve? I found my valve in my 96A3 to be VERY simple to take apart and clean and put back together. You may just have "junk" stuck in the valve ports and a good cleaning may be all you need.

DavidInWilmNC · October 23, 2007, 04:56:09 AM

Hi Brian,

It looks easy to take apart... at lease from the manual. I'll pull it out and see how it looks. I'll check with Luke and see if any rebuild parts (diaphragm, etc) are available for it. Thanks.