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Old 06-02-2020, 08:50 PM   #1
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Dash Air trouble shooting

We have Over The Road Air Conditioning in both the bedroom and the drivers area. The bedroom one works fine, I think the drivers area one doesn't work because the hot water for heat never shuts off. The water lines are too hot to touch going into and out of the air handler. The OTR AC is just one big system with one engine powered compressor so if the bedroom one works the drivers area one should work too. I have not checked the charge on the system this year but the condenser unit in the bedroom makes cold air and generates condensation so I know the compressor is working.

The drivers AC unit was manufactured by "Specific Climate Systems" which appears to have been purchased by Victory Climate Systems.

I'm trying to find a trouble shooting guide to help figure out why the hot water valves aren't closing or what exactly the problem I'm experiencing is caused by. I'm guessing the vacuum isn't being routed correctly from the control unit to the valves. ??
Fred
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Old 06-02-2020, 09:36 PM   #2
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With a rear diesel, note that in that era, and in both my '94 & my '02 diesels, they had shut off gate valves right at the engine. That makes sense if you think about it. That heater hose went all the way from the engine up to the dash and back. So you'd want some safety feature like those valves. Just shut those off at the engine as a test (follow the heater hoses back from the dash area to find them). Many diesel pusher owners shut those off in the spring and back on in the fall. Others put 3 brass valves plumbed in to bypass the heater core under the front hood as they're easier to get to than the engine valves. Techs often forget to turn them on when they flush the radiator and every winter you read about complaints of no heat.

I always thought if I was going to do that under the hood thing, I'd just use one valve on the incoming water supply to the heater core, just to shut it off. It's a closed, pressurized system so I doubt water will flow backwards in it via the output hose. Even if it did, nowhere for it to go and I'd think it would take a long time for any 'hot' water to somehow circulate passively in and out of the heater core.
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Old 06-03-2020, 05:10 AM   #3
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Fred, my 2000 Magna does not have shut off valves for the front dash heater hose. If you still have the bus pumps, one near engine the other up front, then you can disable those and see if that helps. On my coach i rewired the circuit for the bus pumps and installed a switch so I can turn them off or on as needed.

Those pumps run anytime the coach ignition is turned on. I've read in other posts that some have installed a valve on the hose going to the dash heater but I would think you would want to turn those bus pumps off if you close the valve.

On my coach there is a 20 amp 12 volt circuit breaker on the front run board that provides power to the bus pumps and, if you have them, the heated mirrors. Those wires are #134 for the pumps & #78 for the mirrors and are on the 3rd circuit breaker down from the top on the center column of fuses on the front run board. You can pull that breaker and see if disabling the pumps help. If so then you can plan any further action you want to take.

I'm sure others have attacked the problem in different ways and will post alternate solutions.
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Old 06-03-2020, 07:59 AM   #4
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Yes our Magna doesn't have valves either. Shutting off the pumps is a good idea I'll track down that fuse. I've considered installing a valve but have not taken the time to locate the correct hose. With the Webasto system it appears there are four hoses to the front. Two for the dash heater and two for the front heat exchanger.
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Old 06-03-2020, 10:02 AM   #5
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Pete our Magna is wired the same way. I pulled the breaker, labeled it and set it aside for now. Researching the SCS/Frigette dash system I see that the water valves are normally open and only closed when "Max AC" is selected so that might explain why everything I touched in there was hot. So I'll run it on Max AC and leave the breaker out on Friday when we take our next trip. Also, I'll throw a can of Freon in to make up for what may have leaked out over the winter. Our dash system has never cooled like the one in the bedroom and I'm sure its all the hot water from the engine circulating through there.

How did you wire the switch in to the pump circuit?

Fred
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Old 06-03-2020, 10:36 AM   #6
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Fred, I had the same problem on the '04 Allure I owned and now my '03 Magna. I solved the problem by putting a common woodworking clamp on the hose supplying hot coolant to the HVAC heat exchanger. Installed clamp in spring and removed in autumn. I have since installed ball valves and removed the bus pump. So, now I close valves in spring and open them in autumn. The clamp worked just as well.

Good luck Fred.
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Old 06-03-2020, 06:20 PM   #7
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Fred, see my post in this thread. About the 5th post on first page.
https://www.irv2.com/forums/f112/ove...ng-376104.html
If you have further questions, pm me.
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Old 06-03-2020, 06:28 PM   #8
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Having the heater valve fail and pass hot coolant when A/C is selected is a common problem.
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Old 06-04-2020, 07:40 AM   #9
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OK I see thanks for the detail.
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Old 06-04-2020, 07:44 AM   #10
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Update for you all. Yesterday I removed the breaker for the pumps and also clamped the supply from the engine to the dash unit. I then started and ran the engine up to operating temp and added two cans of 134a to the system. I now get 40 degree air from the bedroom evaporator and 80 degree air from the dash evaporator. Water lines into and out of the dash unit are cool to the touch. I'm thinking maybe I have a problem with the AC unit in the dash ? Maybe the expansion valve? It is installed right where the freon lines enter and leave the evaporator coil. - Thoughts? I'm not a refrigeration guy.
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Old 06-04-2020, 09:47 AM   #11
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Assuming the front and rear evaporator coils are piped in parallel and there isn’t a separate dryer in the liquid line going to the front coil I would agree the front expansion valve would be suspect. They are reasonably cheap at Napa. I would leak check your system if you are loosing refrigerant. I would replace the dryer if the system has been flat on refrigerant install the new expansion valve pull a good vacuum and weigh in the correct r134 charge and you should be in good shape. Also make sure the dash blower is moving all the air thru the evap coil and not bypassing air thru the heat coil even though you have corrected the hot water flow thru the heat coil.
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Old 06-04-2020, 10:59 AM   #12
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Roy thanks for that. Yes they are in parallel and there is only one receiver/dryer. I had not thought about air flow. I just assumed the system blows the air through both the evaporator coil and the heat exchangers. I'll manually operate those deflectors to see if any change occurs. The front expansion valve gets cold and even a little frosty. Thanks for the suggestion.
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Old 06-04-2020, 01:10 PM   #13
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Quote:
Originally Posted by Fredward View Post
Roy thanks for that. Yes they are in parallel and there is only one receiver/dryer. I had not thought about air flow. I just assumed the system blows the air through both the evaporator coil and the heat exchangers. I'll manually operate those deflectors to see if any change occurs. The front expansion valve gets cold and even a little frosty. Thanks for the suggestion.
Fred

Interesting that you only have one dryer. My old Magna has two evaporators, expansion valves, and Dryers for the OverThe Road AC system.

Our second one of each item is in our overhead cabinets in the Bedroom next to the evaporator fan that blows cold air into the room.

The dash dryer is located in the engine compartment.

Not important if you already verified your unit is different.
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Old 06-05-2020, 09:19 AM   #14
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Yes our bedroom evaporator is a Red Dot (I think) and it has an expansion valve but no receiver/dryer. And there is definitely not a receiver/dryer up front. I replaced the dryer two years ago when we replaced the compressor.

The front evaporator has never cooled like the bedroom one but I always assumed it was because of hot water being present. Now even with no hot water it's only making 80 degree air and the ambient temp is 80. (used to make 65 degree air).

I'm checking on a replacement expansion valve. Looks real fun to replace tucked away up under everything in the dash!
Fred
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