Miller M1MB 070ABW Pressure Switch Open

[JoeM]

Strange situation. My furnace will being its cycle and the pressure switch will flash "open". Thinking it was the switch, I have replaced 4 of them. The last time the switch indicated "open", I jiggled the terminal lead and the light was solid and the furnace fired. I had the leads professionally replaced but it did not fix the issue.

What other items should I be looking for? As I stated, the switch flashes open but will go to normal if I reposition the leads. I furnace will cycle a few times normally but will eventually return to the open position. Very frustrating.

Any info would be appreciated.


Miller Model M1MB 070ABW Serial # M1D021003824

[Robert]

Hi,

Test both terminals to ground for 24vac, should have it on one for entire cycle.

Be sure tubes are tight, not kinked and unclogged.


Be sure air pipe to combustion motor is clear.


Be sure motor is running strong and smooth and motor and wheel are clean.



Thanks,
Robert