RV Furnace

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Old 03-10-03, 05:24 PM
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Question RV Furnace

I have a furnace i took out of my camper that never worked since i bought it last year. It a 1983 camper with a Duo Therm model 65925-064 furnace in it. At first the thermostat when turned up, clicked the relay and nothing happened. So I took it out and looked it over and was going to buy a new blower motor but ended up cleaning and lubricating that one which in turn worked, Now when the thermostat is turned on, the motor starts and you can see the the electronic ignition thru the site glass wanting to ignate the propane but nothing is happening. I know theres gas to the valve, now the question is, is it the valve or the circuit board? Which is a most likely suspect and what is the best way to test it? Or should I take it somewhere for servicing? Thanks. Joe
 
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Old 03-10-03, 05:57 PM
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may want to take it to the dealer

i would look for voltage to the valve, not sure what voltage to look for in your case, never worked on one of those, may be millivolt.
 
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Old 03-10-03, 06:54 PM
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We have worked on many RV furnaces, including DuoTherm. Depending on your circuitry your problems can range from a sail switch failure to a regulator failure.

First, check the sail switch if you have one. The sail switch is an on/off device. (normally in the off position) It gets it's name from the "sail" or paddle that is attached to the switch mechanism. As the blower comes up to speed, it blows air onto the sail with enough force to push the switch closed, thus allowing electrical current to flow to the next component in line.

It's job is to determine if there is adequate air flow for proper combustion to take place. If the battery voltage is low or the fan does not come up to 75 per cent of it's design speed, the sail switch will not close.

Possible causes of this malfunction are: low battery, restricted return air inflow, restricted or inadequate outlet vents, restricted combustion air inlet or exhaust, faulty sail switch.

If the switch is ok, then check to see if there is a limit switch that might be interupting power to the circuit board. (some models allow the blower to run as a safety precaution even with power interrupted to the board)

Next, check for proper voltage at the circuit board. The circuit board will not receive power until the sail switch is closed by adequate air flow from the blower. The power must also flow through the limit switch.

When the circuit board is triggered by this current, it usually delays ignition for about 15 seconds to allow the blower to purge the combustion chamber of any unburned gases.

The circuit board then sends voltage to the ignitor assembly to ignite the gas/air mixture. At the same time, the circuit board sends power to open the gas valve(s) allowing the fuel to flow to the burner, after which, the circuit board monitors the burn cycle through a sensor that detects the presence of the flame. If the sensor does not detect a satisfactory flame within about 10 seconds, the board then shuts off the gas valves and discontinues the ignition spark. Depending on the board design, it will probably try for ignition up to three times. Beyond that point, it goes into lockout mode, will not retry for ignition until reset and the blower will continue to run.

If you have the correct at the circuit board, check for the correct voltage at the gas valve itself. If you show power and the valve is not allowing gas flow...replace the valve. If you don't have power at the valve...replace the circuit board.

Hope this helps you...please let us know what happens

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Old 03-10-03, 06:59 PM
firsthvac
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Two other notes:

A. If your sail switch is not closing, it could be your motor is not turning fast enough to provide the airflow needed to close the switch.

B. If you have a White-Rodgers Dual Coil gas valve, you can check the resistance (ohms) of the coils. Each coil should have 30-50 ohms and can be replaced individually instead of buying a complete valve.
 
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Old 03-12-03, 05:00 PM
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coils on gas valve

So far, I've determined that the gas valve is at fault.I have the "Johnsons Controls" dual coil on my gas valve. You mentioned about removing the coils and replacing them. It looks like there are 6 screws holding the top plate of the gas valve along with the two coils. Should i take the top plate off? If not, how can i get the coils off? There doesn't seem to be any other way.
Thanks.
Joe
 
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Old 03-12-03, 06:13 PM
firsthvac
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Coil replacement was only recommended for the White-Rodgers dual coil valve since the coils can be removed individually. Considering you have a Johnson Controls valve, replace the valve.

Let us know what happens
 
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Old 03-14-03, 08:18 AM
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Two questions i have, first, i called johnson controls and they don't make that valve anymore, any suggestions where I can buy one?
Second, being that theres 12 volt coils on it, is that what i should be reading on it? 12 volts?
thanks,
Joe
 
  #8  
Old 03-17-03, 07:37 PM
firsthvac
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My apologies, Joe, for not getting back to this sooner. Had to go to D.C. for some business over the weekend. To answer your questions...1) yes, you will need a valve with the same voltage 2) you should be able to find the valve (or it's replacement equivalent) at a reputable RV supplier. If not, they should be able to direct you to someone that has what you need. We use the following supplier. I don't know if they will have the part, but they can probably direct you to someone who does.

Coast Distribution
1982 Zanker
San Jose, CA 95112
tel: (408) 436-0771
fax: (408) 436-0670
Products: Full Line RV Parts/access

Hope this helps.
 
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