Need HVAC advice, my heater inop. (1 Viewer)

[Steve Schaffer]

I have an intermittent problem with my central heating system and now that it's cooled off again it's back.

I have a Carrier "dual pack" HVAC unit, roof mounted. This is a heat/AC unit in one box up on the roof.

When it is functionning properly and I turn up the thermostat, I hear a faint hum overhead, not the regular blower but a quieter one. This is followed in a few seconds or so by a clicking or sparking sound and a "fwoomp" from the gas lighting. The gas runs for a while and then the main blower comes on.

Right now, when I turn up the 'stat, I get the low hum and that's all, no click/spark, no "fwoomp", no heat.

It's my uninformed theory that the low hum is a blower pulling down the atmospheric pressure in a burner housing or something like that, and that when the pressure drops the spark is an electronic igniting device. So possibly the burner housing (if that's the right word for it) doesn't seal, or the pressure sensor is bad, or the spark igniter is bad.

If anybody out there is an HVAC expert I'd appreciate any feedback.

I have an appointment next Monday to have it checked out, and just hope it keeps malfunctionning until then so they can diagnose it, but in the meantime I'd like to know a bit more about how these things work and what the most likely problem is, not to mention the cost of repair. I only use 2 rooms in the house and have electric heaters for them so I'm not gonna freeze, but would sure like to get the central system back on line.

The unit is about 15 years old, cools fine in the summer, but has had this intermittent heating problem the last 2 winters (this'll be the 3rd)

TIA for any help or advice!

 

[Philip_G]

Hot surface ignitor died, or a problem with the polit/ignition system.
or, problem with the pressure switch or an obstruction in the vent. 99% a hot surface ignitor/ignition though. It might be a little old to have a HSI.

 

[Steve Schaffer]

Thanks Philip. Darn thing kicked on about 20 minutes ago, so it's not completely dead and now I gotta cancel the repair guys.

I fix cars for a living, and in most cases an intermittent problem like this can't really be accurately diagnosed if it can't be duplicated by the service tech. Now I know how frustrated some of my customers can be, but can sympathize with the HVAC people not wanting to throw parts at it without duplicating the problem.

 

[Philip_G]

that's something else then, maybe a problem with the draft inducer or pressure switch. Heck, could be a gas valve I guess too. Hop up there and look around, they're not that complicated.

 

[Steve Schaffer]

I just might do that. I think the repair place would be justified if they sent me a bill anyway--I called and canceled with them 3 or 4 times last winter 'cause the thing started working again on it's own (always with plenty of notice so they didn't lose out). Seems like all I need to do is call for a repair appt. and it starts working within an hour or so, even if it's been totally inop for 2 days previously.

 

[Philip_G]

it probably has a pressure sensor on the flu, looks just like one on a car, round metal thing with 2 spade connectors, next time it won't fire jumper those together and see if it goes, if that doesn't close it won't open the gas valve. if that doesn't do it give the gas valve a good wrap with a wrench or something and see if it clicks open.

 

[Steve Schaffer]

Thanks Philip, really appreciate the advice.

If you ever have a Toyota related question I'm your guy!

 

[Philip_G]

want to come help me swap a 5efhe into my GF's paseo?