Furnace will not run

[JJB]

Nordyne model M1MB 090A BW
serial:M1M990901972
Unit works great on A/C but when you go to heat, you can hear 1 click in the area of the circuit board and the light flashes twice indicating that the pressure switch is open. I checked the voltage to the pressure switch, negative reading, supposed to be 24 volts but no power to it. So do i need to replace that entire circuit board or is there another test I can do? Thanks

[Robert]

Did you test across the two switch terminals on pressure switch ?

Should be 24vac there and 0vac if/when the switch closes.

The diagnostic light is indicating the switch is not closing, this has nothing to do with the wire terminals or the 24v circuit.


If the combustion motor is running strong, the inlet air pipe is clear with no damage and the tubes connected to pressure switch are connected good and tubes clear, then the pressure switch would be most likely suspect.


Pressure Switch # 632453 @ $27.42 + $6.75 shipping .


It can be seen and ordered from here:

http://www.mobilehomerepair.com/NordyneGas.html



Scroll down to locate, click on pic for enlarged view.


If interested, please add to cart and order through PayPal or call toll free to 1-877-263-7860 and charge to Visa or Mastercard.


Thanks.


Take care and best wishes,
Robert

[Robert]

Just wanted to add, if the press. switch is not getting the 24v signal, that would be a second problem.


Test across board terminals 24V - COM for 24vac.

Then disconnect the 9 pin molex plug and test pins 5 and 6 for 24vac.

Then test the two orange wires at the pressure switch for 24vac.




Thanks,
Robert

[JJB]

I forgot to mention when it clicks that there is a humming/buzzing sound coming from the circuit board area, i did check the tubes and checked that air flowed freely into the pipe. I did buy a pressure switch from you and by the way great fast service on your part, but i do not hear the combustion motor. when i turn the switch on i get 1 click sound like a relay and then the humming sound and then the blinking code lights Thanks again

[Robert]

Unplug the connector plug at the combustion motor. Set t-stat to call for heat, at call for heat wait about 2-3 seconds, then test for
120vac at the plug that comes from the board.

If you do not have 120vac there, go to 6 pin molex connector at board, disconnect and test across 1 and 4.

You may have to turn off, wait 5 minutes or so and try again in between each test to prevent lock out.


Now, if it was flashing two flashes, combustion motor should be running, be sure it is not.

If you do not have 120vac at 1 and 4, test across XFRM terminal and first NEU terminal beside the XFRM.

Getting late, I'll check again tomorrow when I can.


Thanks,
Robert