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Phil
Phil, Mechanical Engineer
Category: HVAC
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Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I have a Lennox MPE 36R unit Model H534. It is wired volts.

Customer Question

I have a Lennox MPE 36R unit Model H534. It is wired for 240 volts. Everything works except the heating elements. It is about 3 years old now. The first year the heat worked fine. I replaced the main control board just now. I can get 120 volts to ground at each connection point on the heating element but I can't get 240 volts between the orange (L2) and the red wires (load side of relays). There is 120 volts to the control board, I can hear the relays pull in when the switch is activated.
Submitted: 1 year ago.
Category: HVAC
Expert:  airheatman replied 1 year ago.

Are you getting 120v from L1 on board where power connects on board, to a ground?

Expert:  airheatman replied 1 year ago.

Power in to board

Customer: replied 1 year ago.
the fan works, the lights work. And I have 120 volts to the neutral as well.
Expert:  airheatman replied 1 year ago.

OK next coming out of the control board , do you see a limit switch before wire goes to element? And if so, lets check between the orange L2 and each side of the limit for 240 volts

Customer: replied 1 year ago.
If you are referring to the overtemp limit switch then yes. There is 240 volts from the orange wire to either side of the switch.
Expert:  airheatman replied 1 year ago.

Ok but no 240 if you place one lead on each terminal of element?

Expert:  airheatman replied 1 year ago.

Can you take a pic of the wiring to elements and attach here?

Customer: replied 1 year ago.
Correct. There are 2 red wires (from the relay on the board) that connect to one end of each element. Should be L1 right? But there is no 240 volts from either red wire to the orange wire (L2). But there is 120 volts to ground on each. Almost like it is all the same phase.
Expert:  airheatman replied 1 year ago.

Can you take a pic of the wiring to elements and attach here?

Customer: replied 1 year ago.
See if this works
Expert:  airheatman replied 1 year ago.

Yes but a bit close. trying to see where wires come from.My manual does not show me colors of wires.

Customer: replied 1 year ago.
How's this?
Expert:  airheatman replied 1 year ago.

That is better, but I still can not tell exactly where each wire is coming from. I have not personally worked on this particular unit although I am familiar with many of the Lennox units, juts never worked on one like this. I feel it in your best interest that I opt out and see if another expert may be more familiar with the unit.I have opted out of the question to see if perhaps other experts may have more information and can assist.Please do not rate or reply as that will send question back to my desk.Please stand by to see if another expert can assist further.Thanks for allowing me to work with you to this point.

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