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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I have an older carrier furnace, installed in the 90s. I

Customer Question

I have an older carrier furnace, installed in the 90s. I would like to troubleshoot why my furnace is not reaching the temperature on the thermostat before shutting off. It's a vertical furnace located in my crawl space. Just replaced the filter. It seems to have always been that way for years on cold days. It runs for a minute or two and then shuts off and turns back on a few minutes later. Suggestions? Questions? My husband services it as needed. He is not an hvac specialist but a general handyman, so he doesn't have much experience with why it would be shutting off and back on
Submitted: 8 months ago.
Category: HVAC
Expert:  airheatman replied 8 months ago.

Sounds like a high temperature limit switch is opening and closing.

Does furnace have a control board in blower compartment?

Can you give me the complete model number on the furnace?

The number on outside of furnace is just a series.

Actual model will be on a label on inside furnace panel just above burners.Remove panel to burner compartment and look inside. The model number will help me give accurate assistance for your specific unit.

Below is a link to a generic video showing where to find label with model number:

Customer: replied 8 months ago.
Two pics include complete model # and prior servicing.
Customer: replied 8 months ago.
Customer: replied 8 months ago.
As I was down there I sat there and listened. heard it fire up, seeing the coils glow and the blower motor run. Then the blower motor continues to run as it should and the coils kickback on when needed To reheat but for some reason it shuts off and wait a little bit before it kicks back on even if target temperature is not reached. How long should it run before it needs to stop and "cool down"?
Expert:  airheatman replied 8 months ago.

1. How long do burners stay on before shutting down?

2.Does blower keep running entire time?

Customer: replied 8 months ago.
I'm reading up on the furnace. I have all of my registers open now too. My upstairs was closed off, but like I said, it's been like this for years. Maybe junk build up? I had issues with the limiter and it was a diff problem. All my coils fire and are glowing for approximately 2.5 minutes then the blowers ran for 4 min without the flame, then flame kicks back in and repeats. Then it will completely shut off, fan and all for few min before starting up again
Expert:  airheatman replied 8 months ago.

When furnace burners are off and should be on check all limits to see if one is open

Customer: replied 8 months ago.
Is the process of the burners being on for 2-3 minutes normal? Or should they stay on the entire time? We seem to go thru igniters every year or two.
Expert:  airheatman replied 8 months ago.

Burners should stay on continuously until thermostat is satisfied