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cptmiker's avatar
cptmiker
Explorer
Mar 25, 2017

duo therm 65920-042

Hello All I am sure this has been asked alot but I cant seem to find what I am looking for, searching posts.

I have an older late 70'S duo therm 65920-042 is in descent shape very little rust. I'm looking for a replacement Gas Valve. the replacement I have found is listed below.

RobertShaw-Millivolt-RV-Gas-Valve-24V-12V-7000ELC-736-505-528-710-401

This is listed as a direct replacement. But it is missing one port for the vent. Any ideas ? Has anyone replaced the gas valve and if so what did you use and how did you do it. I know I am going to get a few that are going to tell me to replace the unit. I would if I could find one that I don't have to cut new holes in the fiberglass siding. of the RV.

I have tested all the electrical parts on this unit and they all test within spec but the gas valve for the bummer is not opening working properly. Kid of expected to a 36 year old unit.
  • cptmiker's avatar
    cptmiker
    Explorer
    Mar 26, 2017
    There is no plate but yes there is a limit switch there but screwed directy to the cabinet. I will try it. and update
  • Chris_Bryant's avatar
    Chris_Bryant
    Explorer II
    Mar 26, 2017
    If yours has the limit switch right above the gas valve- like a 1x3" plate- that is the most common failure for that model. I would try *temporarily* bypassing it to see if that helps.
  • cptmiker's avatar
    cptmiker
    Explorer
    Mar 26, 2017
    Well I spoke too soon it is now randomly working I have 12v everywhere except accross the gas valve which seems to be randomly at 12v and it works and then most of the time its at .5 to 1.2v any thing else I can check to see why it will randomly not apply 12v across the gas valve. I have 12 volts across the Limit switch. witch connect to the gas valve. and the thermostat switch on the other side. I also checked the thermostat switch and I Have the same voltage comparison as above.
  • cptmiker's avatar
    cptmiker
    Explorer
    Mar 26, 2017
    Ok looks like I got it to work. I tested the power from the old Converter barely putting out 11v. Removed converter and replaced it with a new Progressive Dynamics PD9155 and a Parallax Power Supply FB9 Fuse Block and rewired all the DC connection. Rechecked all the wires on the furnace and replaced all the Wire twist connectors on the furnace cleaned all connectors and put everything back together and Tada its now working without changing the Gas regulator on the furnace.

    I checked the Old Power converter out of the RV with a load of 2, 12V lights and the voltage was still 10.8 to 11v. its was also 37years old. So now a more efficient system is now in place.
  • cptmiker's avatar
    cptmiker
    Explorer
    Mar 25, 2017
    Thanks Chris

    I have tested the sail switch with the unit out of the RV by connecting a fully charged 12v battery to the unit with out a gas line. Sail switch is open no connection with out power, then power applied. fan spins up sail switch engages and makes full contact and closed allowing power to flow. There seems to be two limit switches on this unit one in the front of the enclosure and one inside mounted to the frame not next to the burner. as well as a relay for the motor. I will recheck voltage to the gas valve across the two pins. yes it is a pilot model and the pilot lite works as it should. If I have voltage across the two connector on top of the Gas valve the manual says to replace the valve. MY concern is that extra connector. the say's return on the current valve. Can I omit it will it cause an issue since the new valve does not have this connection
  • Chris_Bryant's avatar
    Chris_Bryant
    Explorer II
    Mar 25, 2017
    I assume your is a pilot type- don't worry about that vent tube, that valve should work fine but...
    If the pilot does light, but the main valve will not open, verify the voltage you are getting at the valve. I suspect between the thermostat, sail switch and limit switch, you are loosing too much voltage.
    I do have service manuals for that model on my service manual page- see both the 659 and the pilot type sheet.

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