STRANGE CARRIER issue

[fattogatto]

I have a relatively new (18 month) Carrier forced air furnace. New filters, clear vents, drain clear. Whenever the outside air temp gets below 20 degrees for any length of time the unit shuts off. I can instantly restart it by either cycling the power switch off-on or by removing the panel which opens a continuity switch. Then I reinstall said panel and the unit fires back up. It stay on for 2 - 4 minutes and then shuts down again. There are 2 panels - one that covers the blower and the circuitry (board) which has the LED indicator light showing error codes, and the other panel covers the combustion chamber. This second panel has no continuity switches associated with it. It has a forced air vent (6" PVC) and an open tube (also 6" PVC) that seems to simply vent that chamber to the air in the attic. My dilemma is that (1) the unit runs perfectly if the air temperature is above 20 degrees F. AND/OR, (2) if I remove the panel covering the combustion chamber the unit works perfectly regardless of air temperature. It is definitely temperature related. The error codes say it might be a myriad of problems. Possibly by removing the panel I am changing the temperature/pressure of the air in the chamber?

By the way, the unit is installed upside down due to the supply coming from the attic and the ducting all being under the house through the crawlspaces. I mentioned this to the gent who installed it and he assured me it was perfectly fine in either orientation.

Any help out there? Thanks.

It looks like it is a high pressure switch failure. That's the route we're taking as soon as the roads clear.

 

[Crazyjake8493]

Was this installed by an HVAC company or some guy who just managed to get his hands on a furnace?

Are you sure the PVC pipes are 6" ?

Is the unit itself located in the attic?

 

[fitter30]

Burner control has failure flashing light which shows what it is. Take a pick of the unit and complete model#? Burner should be accessed without blower door being removed.

 

[fattogatto]

Installed by qualified company. Yes, 6" PVC that goes up into the attic. Unit has been working all night and today. Seems like the magic trigger temperature is about 15F. The code (3 - 1) indicates a high pressure switch that measures the pressure inside the chamber. I'm guessing the extreme cold temperatures increase the air density just enough to trigger the valve which shuts off the gas. I'll have valve replaced when tech gets here.

Unit is located on ground floor in an old closet. Intake comes from on top with the heated air going down into the duct system.

 

[Crazyjake8493]

Something sounds off here. High efficiency furnaces should have two PVC pipes - one for combustion air intake, and one for exhaust - and both should terminate outdoors. If anything I hope only your intake is terminated in the attic and not the exhaust.

They are also typically 2" or 3" pipes. I have NEVER heard of a unit using 6" PVC pipe unless I'm missing something.

Code 31 on a Carrier is a pressure switch failure to close (or re-opens after closing). This closes upon correct draft of the unit by airflow in through the combustion air intake into the furnace, through the draft inducer into the heat exchanger, and out of the heat exchanger through the exhaust. If the combustion air intake or the exhaust are obstructed in some way, you will not be able to establish proper draft.

Since it runs fine without the burner compartment cover on the furnace (bypassing the air intake), I would start by examining your air intake. If it really does terminate in the attic, look down through it with a flashlight, or up through it from the furnace with a boroscope camera if you have one. Make sure it isn't obstructed with insulation or a birds nest or something.

It's strange that it runs better in warm temperatures, but temperature alone should not affect this. My furnace (Goodman) combustion intake terminates outdoors (facing snow and wind) ours runs just fine when it's -15F outside.

 

[Wrench97]

That usually means a blockage, ice build up on the top of the chimney maybe?
What fuel N.G. or Propane?

 

[fattogatto]

Fuel is natural gas. Will try to examine the exhaust and intake PVC pipes. My eyes were bigger than my head. The pipes are 4" PVC, not 6". Last night the temps were down to 11F and the unit worked fine all night. It fails when the temp apparently reaches into the single digits. Of course, when the tech gets here the temp is above the trigger point and he says he can't find an issue. I've left all of the pertinent info with the company and they are supposed to call me before coming out to discuss.
Thanks for the advice.

 

[Crazyjake8493]

Fuel is natural gas. Will try to examine the exhaust and intake PVC pipes. My eyes were bigger than my head. The pipes are 4" PVC, not 6". Last night the temps were down to 11F and the unit worked fine all night. It fails when the temp apparently reaches into the single digits. Of course, when the tech gets here the temp is above the trigger point and he says he can't find an issue. I've left all of the pertinent info with the company and they are supposed to call me before coming out to discuss.
Thanks for the advice.

It's not a temperature issue. You started with twenty degrees, then fifteen degrees, then single digits. The temperature thing is in your head. You have a draft/exhaust issue.

I'd have a new HVAC company come out, NOT the ones that installed this. Based on what you've already told us, I wouldn't want them working on anything of mine.

 

[PoorUB]

One thing that happens fairly often is the exhaust swirls around and frosts up the intake. If there is a bird screen on the intake, remove it. Oh, this happens more in colder weather as the furnace runs more and has more exhaust.

 

[4x4Pete]

I had a service call where a similar problem was happening. A few techs were stumped by the problem. It turned out to be related to the drain piping length. It was 1/2" drain tubing run about 40' along the floor running to a sump pump. When the weather became excessively cold, the furnace would cycle more and produce more condensate which couldn't drain fast enough and cause a pressure switch code. A condensate pump mounted beside the furnace with the drain line piped to the sump cured the problem.

 

[Crazyjake8493]

I had a service call where a similar problem was happening. A few techs were stumped by the problem. It turned out to be related to the drain piping length. It was 1/2" drain tubing run about 40' along the floor running to a sump pump. When the weather became excessively cold, the furnace would cycle more and produce more condensate which couldn't drain fast enough and cause a pressure switch code. A condensate pump mounted beside the furnace with the drain line piped to the sump cured the problem.

That's certainly possible, but OP state the unit would run 2-4 minutes before shutting down unless the burner compartment panel was removed.

Using a manometer to check the draft with the cover on and off would confirm or rule this out.

I would hope the tech checked the draft with door off and on but you never know.