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Old 09-21-2016, 10:12 AM   #1
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no dash heat

I've had motorhomes for 30 years, but bought my first DP, a 2003 35' Allegro bus, last August from a Tucson, AZ dealer. Freightliner chassis and a 2136 Cat. I guess it was hard to verify that the cab heater was working when it was 110 degrees out during checkout, because when I got home to Minnesota, no cab heat. With a hot engine, both heater hoses are cold. Both shut off valves back by the engine are open and I have antifreeze at the outlet valve petcock (with outlet shut). There's a vacuum controlled valve at the heater that closes on Max AC, and it operates correctly. I pulled that valve and it is clean and works internally. I also have antifreeze at the vacuum valve. Because the valve is clean inside, I assume the heater core is also good. Is there a water control valve inside the heater that modulates the heater temp? Or is temp controlled with blend doors?

I'd bring it back to the dealer, but am not planning to return to AZ until January. Any suggestions as to where to turn next?
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Old 09-21-2016, 10:31 AM   #2
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Quote:
Originally Posted by Tahoejeep View Post
I've had motorhomes for 30 years, but bought my first DP, a 2003 35' Allegro bus, last August from a Tucson, AZ dealer. Freightliner chassis and a 2136 Cat. I guess it was hard to verify that the cab heater was working when it was 110 degrees out during checkout, because when I got home to Minnesota, no cab heat. With a hot engine, both heater hoses are cold. Both shut off valves back by the engine are open and I have antifreeze at the outlet valve petcock (with outlet shut). There's a vacuum controlled valve at the heater that closes on Max AC, and it operates correctly. I pulled that valve and it is clean and works internally. I also have antifreeze at the vacuum valve. Because the valve is clean inside, I assume the heater core is also good. Is there a water control valve inside the heater that modulates the heater temp? Or is temp controlled with blend doors?
I'd bring it back to the dealer, but am not planning to return to AZ until January. Any suggestions as to where to turn next?
.
Tahoejeep
On some coaches the "hot/cold temperature regulating valve" (which controls the flow of coolant through the heater core) is controlled by vacuum, (just like the blend doors).
(On my coach that valve is controlled by a push/pull cable).
Mel
'96 Safari
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Old 09-21-2016, 10:48 AM   #3
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Welcome to iRV2.

I'm sure your Cat engine series is 3126E in 2003.
The vacuum valve that shuts off coolant flow , near the heater housing, would be the last , factory installed flow shut off in the system.
However , that isn't to say that a previous owner didn't add a manual shut off that was easier access than the ones by the engine.
If your dash HVAC system is Evans/Tempcon , (and with a vacuum control) , I'm sure it will be, temperature is varied by internal blend air doors and an extra coolant shut off could have been added to aid A/C operation in normal mode.
If the coolant flow trough the core has been shut down for years , the core may be plugged, so if you don't find an added shut off, remove both hoses from the core , then hook up a garden hose to flush water through the core , keep the flow rate; pressure; low and be ready to catch the A/F that's blown out as the water goes through, if flow through the core is low , reverse the flow , several times to try and clear any restriction.
You could also check the engine's water pump belt tension , a loose belt there can cause poor coolant flow issues.
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Old 09-21-2016, 11:05 AM   #4
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Sounds to me like you are not getting circulation thru the heater loop. I would think both hoses should be warm with a hot engine. Are you sure you haven't overlooked yet another valve somewhere in that loop? My Freightliner chassis, with CAT engine has 2 valves, one in the supply line going to the heater, and, another one in the return line from the heater and this is the same line that has a petcock in it, between the valve and the heater. Maybe you have a 3rd somewhere....The Freightliner procedure for the fill procedure is to close both valves in the heater loop before refilling the system, this will result in filling the engine, but leaving the heater loop empty. Then, with the engine running, the valve TO the heater is opened (not the one in the same line as the petcock, but the other one), along with the petcock. When a steady stream of water exits the petcock, the heater loop is filled. Since your system is filled and those valves are open, some improvising must be done.

My thoughts on a procedure that closely follows the Freightliner one are that you close the valve between the petcock and the engine (this prevent draining the engine side coolant when you open the petcock) and then open the petcock and catch whatever runs out. Shouldn't be a lot, just what is between the valve and the petcock on the engine side, and what is between the petcock and the heater, on the heater side. Not much more than a quart or so, if that much. Now, theoretically, the return line from the heater is empty and the line going to the heater is filled. My heater is higher than the hoses we're talking about (I assume yours are the same) so only the return side should empty...I can't see it siphoning water from the supply side since no air can get in the system. At that point, you close the valve going TO the heater, now both valves will be closed and the only difference between this and the Freightliner heater loop fill procedure is that you have the supply line from the engine to the heater core filled, but with the supply valve closed, this coolant isn't going anywhere until you open the valve. Having the supply line valve closed prevents any circulation, when you start the engine, until you can get in a position to view it. Then start the engine, run it at high idle for a minute or so, then let it return to idle, get under the vehicle and open that supply line valve going TO the heater (not the one in the petcock line) and see what happens. If water begins to flow out the petcock in a few seconds, (the valve between the petcock and engine is still closed), then water is circulating between the engine and the heater. If nothing comes out, or only a trickle, then no water, for whatever reason, is going to the heater loop and I'd be suspicious of a blockage or a kinked/collapsed hose in the supply line. Don't forget to open all valves and close the petcock when finished. :-) The heater bypass you mentioned, working correctly or not, would have no effect on your problem, it simply bypasses the heater core when using A/C or allows water thru the core when heat is desired.

The above is an envisioned scenario that should tell you whether or not you have coolant circulating thru the heater loop. I am not suggesting you do it, it involves being under the vehicle with the engine running and that is always hazardous. It freaks me out to do it on my vehicle and about the time I get under it, worrying about brake failure and the transmission getting into drive or reverse and the vehicle starting to move, the damned air dryer vents off and I nearly have a heart attack!! :-)
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Old 09-21-2016, 11:48 AM   #5
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I have not read all the posts to this thread.... HOWEVER I've worked on several Freightliner Chassis and each has had a gate valve OR ball valve in the return line from the heater core to the engine.. in each case it was along side the transmission on the drivers side of the frame rail...

You have to close this valve and than open the bleeder that is attached to this valve and put a 5 gal bucket under the bleeder valve.... in each case its taken me close to an hour with the bleeder valve open and maybe 10-12 Gal of coolant to bleed off all the air....

I get 2-4 gal of coolant.... and switch buckets.... pour what I've caught back into the cooling system.... I than install a coolant pressure tester and pump the system back up to 15 lbs....

Once this has been done.... the system is good until the coolant is drained again.... in each case, while I was doing this.... I installed a filter and used the element with the modifier to keep the PH balance correct...
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