Nordyne downflow in trailer eating my lunch!

[tinman720]

Hello, I just signed up here looking for some online help I am an HVAC tech in Eastern Montana and this looks like a great community to discuss HVAC topics looking forward to being a part of the online community.

I have been working on a nordyne furnace M1M series and it has been causing me alot of issues. I'm in Montana in the boom area where the bakken oil is bringing in more "high quality" trailers and furnaces in the area than you can count. I work on alot of these units, very seldom do I have a complex issue they are a pretty simple unit, but this one is really tough to pin down.

Furnace begins its sequence of operation, gets the ignitor glowing and right when you hear the relay click for the gas valve, no gas flow, the ignitor goes out and then will try again after a few seconds. Here is the problem it only does this sometimes, It has allowed the house to cool down in the past but will eventully come back on. I have never witnessed this but the homeowner says this happens. It will not throw any codes just retries and usually lights on the second or third attempt. I have tested the gas valve it works great tried the new control board because that is a common problem with these furnaces, and it acted exactly the same.

It hasn't locked out in some time now but she is constantly calling to have me come remedy the unusual operation and I don't know what to do with it as long as it is only having problems sporadically. Has anyone else ever had this problem?

[kangaroogod]

Inlet and outlet gas pressure? Bad board or valve if that falls in line. Without proper tools to measure and verify safety,,, your guessing

[smoke]

No gas exiting the automatic gas valve on first try? But it will light the second or third?
Don't be so quick to replace parts.
The only way to find the problem is to spend time with the unit. When you head the relay click did you have proper voltage at the gas valve?
Sounds like either no voltage energizing the gas valve, weak coil on gas valve or gas valve is mechanically sticking.

~smoke~

[Joehvac25]

Many of times I turn the valve off and on then they fire again, just happened at my rental, cheap ass land lord didn't want to change the part lol. I always replace a customers valve in that situation because I don't want to go back in a month.

[beenthere]

Check pressure the pressure switch is sensing. Your probably right on the line.

[Chris_Worthington]

Ring out the HSI... 45 -75 new, 75 - 100 going bad, 100+ = bad and intermintent

[BigBacardi]

lol...had this happen to me once... on a maytag mid.....the old tstat was lunched.....and dropping signal as ignitor was on...hence no fault code!!!!! it drove me nuts till i tried to jump furnace and it worked every time....

[Helioson]

Years ago I had an old Coleman unit give intermittent actions. Turned out to be a faulty ground. Quick check by rigging a 12 g wire from ground on the board to a confirmed ground nearby. Hope this helps. Good luck.

[TMH58]

The thing with controls many don't get is there is really no significant amount of current introduced until the gas valve energizes. That can cause a spark, or "bounce" of a bad contact, heat anticipator, connection, limit, whatever. The boards are sensitive to vol;tage drop and a boucing contact. So sensitive that the board has, loses, and gets back the call in a second. Sometimes not picked up my a meter. ALWAYS jump out thermostats first, then limit circuits, (only as a troubleshooting technique). Many boards and other components are replaced before these very simple troubleshooting techniques are used.

[timjimbob]

Seen this. Undersize gas line shared with another furnace or water heater. Other appliance is firing and gas pressure drops too low to fire furnace.

[small change]

Gotta babysit that sucker and be ready

I had a carrier that the gasket on the hsi would allow air
to get in and "sometimes" not allow the burners to light off

I had a comfortmaker after hundreds of cycles the gas valve
would get voltage but stick mechanically closed then after lockout.

Unless you start throwing parts at this furnace and guess
you will have to hangout and make this furnace your best friend


Or sell em a new one

[Freightshaker]

Had a similar issue with a nordyne. Brother in laws furnace- called and told me pressure switch closed code was on. I would have him mess with it and it seemed to always fix it so I bought a new pressure switch. Well of course when I get there that is not the issue. It was behaving similar to how the OP said his was. Yet every once in awhile it would throw the code. I didn't have all my tools with me so I checked all the grounds. Cleaned/retightened checked plugs and it has not done it again for two or three weeks.

[tonkatoy9398]

Here's a long shot. Had a Coleman do the same thing, wound up being a spider nest between the gas valve and orfice. Long shot but thought I would throw it out there for you.

[georgelass]

If the intermittent occurrence seems to be ambient--inside--temperature
related, maybe cold spray in a can or nitrogen from a distance to cool
gas valve or circuit board might bring failure. That is assuming it only
happens at night when you're not there. If it happens on warm
days, try a heat gun on each component. Note that over-cooling,
like coating with ice, can make most any circuit board at least temporarily
fail, so don't go crazy. Me, I haven't actually tried this in HVAC, but
it was commonly used in electronics troubleshooting 25 years ago.
I recently bought a heat gun to try on one customer's intermittent problem,
but then we had a couple days of relatively warm weather and the gas
valve wouldn't work at all.