Nordyne M1Mb 090A AW Vacuum for the pressure switch?

[Mobile68]

Hello:

- Draft motor turns on, but furnace fails to start.
- 2 red flashes show the pressure switch is stuck open.
- Borrowed a pressure switch from the place that installed it, but that didn't help.
- Furnace will strike out, wait about 15 minutes, strike out again, wait another 15 minutes, then start and run on the third attempt. In other words, it takes about 45 minutes for the furnace to finally run, but once it stops, It goes through that whole cycle again.

Is my next step to check the vacuum for the pressure switch?

[Robert]

Hi,

Could be the combustion air pipe damaged or leaking, inducer motor faulty, inducer motor wheel faulty/dirty, pressure switch tubes kinked-clogged-loose-leaking, no 24vac signal to pressure switch, incorrect water column pressure at switch.



Or, none of the above.


That is a safety switch error and would be best to have an hvac tech test and properly diagnose.



Thanks,
Robert

[Mobile68]

Thanks Robert.

As a computer tech for 5+ years, I understand your conclusion of "Or none of the above".

Anyway, it seems I've got an inducer venting issue, or a main board issue. The latter is becoming conclusive, as with further troubleshooting, the system will clear the error code and run fine with a power reset.

[Robert]

Is it clearing error code and running fine due to power reset or due to problem resolved ?



Due to safety, thorough testing of all should be done to know for sure what was wrong and more importantly,,,,,,,,why ?



Thanks,
Robert

[Mobile68]

My last post was a little confusing, but I spoke too soon, as simply turning the power switch on and off was only a coincidence that the furnace then fired up.

So, I checked and there is 24vac to the switch, and the tubes are tight and in excellent condition. I've concluded that the switch isn't getting enough vacuum to close.

1) Once I've blown out the motor, should it be oiled?

2) Anything else I should look for when I open the motor housing?

3) If the inducer motor venting is clogged, resulting in too low of a vacuum to close the switch, then why would it work some of the time?

Thanks.

[Robert]

Hi,


1- Some do, others don't. Will have to determine if it is a sealed motor or one with oil ports.

2- No, just ensure all is clean and working correctly.

3- May be intermittently reaching correct water column pressure to close. Or, could be a bad pressure switch not closing and holding always.


Thanks,
Robert

[Mobile68]

Ok, thanks. I'll check it out tomorrow.

- Why is it called water column pressure? EDIT: Never mind, I found out

- I already tried replacing the switch with a new loaner from the installer.

[Mobile68]

Woohoo Robert, I found the problem!

The upper draft fan was so loose that it was close to falling off. I pushed it down on the shaft and it's now tight and spins beautifully. If it happens again, I'll epoxy it to the shaft.

Also, the upper and lower draft housing gaskets are almost non-existent. I'm talking not just a little broken due to me taking the housing off, but rather the gaskets have degraded to dust. I'll call the installer and see if I can the gaskets separately, but if not, what do you recommend I use?

So bottom line, intermittent vacuum to the switch was caused by a loose draft fan, and degraded draft fan housing gaskets.

[Mobile68]

Continued from above.

Well, I thought for sure that was the issue, but I got the fan fixed, installed new gaskets, and that didn't help.

The transformer is putting out 27.7 vac.

I then noticed a the tell tale sign of a component problem. When the board has two red flashes, I noticed a high pitch sound coming from the board. I used a paper towel tube to narrow the sound to a black "box" that measures about 1"x1/2" on the surface. The board has about 5 of those devices (mini transformers?). Anyway, I tapped on one that was nearest the sound, and behold!, the furnace fired up.

So that's where I am right now.

[Robert]

Hi,

Those are relays. Mark (owner of site) repairs boards in his store and I believe can get those for repair.


Call him @ 605-229-2627 to inquire.



Thanks,
Robert

[Mobile68]

Great. Thanks!

It's been about 12 hours since I "tapped" that relay, and the furnace hasn't faulted so far.

[Robert]

You're very welcome, happy to help.



Thanks,
Robert