Coleman HSI Gas Furnace Mobile Home

Flame comes on, but then off 5 or 6 seconds later, consistently, except for the fact that when I first turned it on (it had been sitting cold overnight), flame lasted for a couple minutes or so, before going out. Then it started going out consistently after 5 or 6 seconds.

I cleaned up the remote flame sensor, but no help. Possible that it's still bad?

I know about the flame sensor circuit from sensor tip thru flame, then to ground. I'll be checking that this morning by current measurement in the flame sensor circuit, but not sure about the acceptable range. 2 to 10 microamps dc?

If I wanted to be sure of good ground from cabinet to control board, where would I hook up a jumper wire at the control board?

Thinking I could follow the flame sensor wire from sensor to control lboard and confirm voltage at that point (from the board), but don'lt know what voltage I should get? Whatever the correct amount is, if I'm not getting that from the board, replace the board?

 

A model number would be helpful as the minimum flame sensor current varies greatly.

Things that affect ground.......
The screws that hold the burner in place.
The screws that hold the control board to the metal frame.

 

Model # DGAT056BDF, HSI, with remote flame sensor. Propane burner.

Replaced both the flame sensor and control board. No help, same symptoms. Pressure switch was changed 2 weeks ago. I waited till the combustion air motor was running, then pulled the wires off the pressure switch, jumpered them together (was advised to try this) - system started up and operated normally.

Installed a different new pressure switch and the same symptoms returned. The 2nd new press. switch was the same part number (on the switch) as the 1st new switch that was in the furnace, but don't know for sure if that number is the OEM spec or not. Hope to find out this morning with supplier. Coleman's/Stylecrestinc.com website/HVAC Service Documents

HVAC Service Documents | Style Crest

did not list a part number for the pressure switch. Part# on the box of the 2nd new press switch is: S1-32435972000. Part# on switch label (both 1st & 2nd switch): 51341. Label on switch: 0.10" WC. I have a new Fieldpiece digital manometer with a tee fitting, but not sure how to hook it up to switch yet. Will give it a try this morning.

If the combustion air motor/fan were pulling insufficient or borderline amounts of air (dirty fan blades, partial blockage in air duct or roof vent), that would cause the same problem, yes? (flame on, then off 5 or 6 seconds later, sometimes not taking that long to go off, sometimes clicking back off as soon as it comes on).

 

If you're combustion blower and pressure switch we're bad you wouldn't get gas valve opening. Try reading volts at gas valve. See if you are dropping volts.

 

Yes..... the pressure could change in the exhaust/flue and cause the burner to shut off. Usually there is enough pressure to overcome those variations.

Put a volt meter on the pressure switch wiring. If you read 24vac then the switch is open. No voltage means the switch has closed.

 

I'll have to check it your way (voltage at the terminals) when I go back, but this morning I installed this suspect switch in another furnace that has the same switch spec'd for it. Worked good. So, on the problem furnace, I separated the combustion air motor from its vertical duct to check the fan and duct for dirt/debris. Found nothing, but didn't go up on the roof yet. Only after leaving that home this morning did I think of running the combustion air motor while I had it disconnected from its ductwork, which would have told me if there was blockage in duct higher up than I could see, or in the roof vent itself, correct?

After I re-attached the combustion air motor to the ductwork, I ran it again and put a clamp meter on one of the wires powering the comb. air motor and it read way below the .67 A spec on its motor/label. I should have written it down, but it could have been as low as .15 A. I've checked other motors with my clamp meter and I just remember that this one was way below the .67 A spec. I was tempted to replace the motor, but was not sure about motor amps behavior when there's a restriction to its air flow.

However when the combustion air motor was running, I removed the wires from the control board to the switch (removed them at the switch) and there was no continuity between switch terminals. Again I jumpered together the wires coming from the control board (while they were disconnected from the switch) and the furnace worked great again (this is about the fourth time I've done that). As I mentioned in my original post, there is both a new flame sensor and new control board (direct replacements) in this furnace now.

Sound like an air flow restriction or a weak comb. air motor to you all? Thx much for your replies.

Could an air flow restriction cause that motor to drop that far down in amps?