Question
I have a Keeprite N9MP1075B furnace with a fan that won't shut off. The AC starts and stops as required, I tried the heat as well and it comes on and off no problem, but the fan will run 24/7. The fan switch is on auto, not on, and even tried a different thermostat and had the same results. I have read that I may have a stuck fan relay and try giving it a tap to loosen it up but I can't seem to locate it on my system. I have been told I might have to replace the board as the fan relay may be located there, the circuit board is ST9160B 1084.

Follow-up
I called a "pro" and he came in for about 5minutes and told me I need a new board.

Last night I did some more reading and went back to the furnace, found the fan relay, gave it a slight tap and the fan shut off. So far the AC has running normally with the fan shutting down as it should. It looks as though everything is working fine for now....with the same board.

Question
I'm troubleshooting an 80% furnace with an IFC board and its inducer blower motor stays on constantly even though the thermostat is set on Off and the fan on AUTO.

Answer
Check the limits. Relay board contacts might be arc together remove the W wire off the board that is your heating call see if the relay drops the ID out. There is a relay that sends power to that motor. It is probably on that board. The contacts have welded themselves together. You might get that to release by tapping the handle end of a screwdriver on that relay, but even if that works you need another board.
Higher pitched "squealing" sound may be caused by slipping blower belt or motor or shaft bearings in need of oiling
Lower pitched "rumble" sound may be caused by a poorly adjusted pilot light if this problem occurs with the burners off.
Lower pitched "rumble" sound may be caused by dirty gas burners if the problem occurs with the burners on.

Possible Repairs
• Oil blower motor lubrication ports (usually at each end of shaft) with light weight oil
• Check for proper belt tension. Belt should depress about 1" at center of span.
• If too loose, tighten belt.
• Replace frayed belt.
• Adjust pilot light
• Call furnace service technician to have burners adjusted or cleaned.
The burner in your gas furnace is ignited either by electronic ignition as found in most modern furnaces or with a pilot flame common in older style furnaces. The gas furnace standing pilot (flame is lit all the time) is sometimes referred to as a pilot light, but no matter what you call it, its purpose is to serve as a small ignition flame for the gas burner. And when this little flame fails to operate properly or go out, it's one of the most common reasons a gas furnace will fail to operate.
So as they say, good things come in small packages and the furnace pilot is no exception. This standing pilot flame (and its friend the thermocouple) makes or breaks your furnace's operation, so it's worth spending some time to learn how it works and how to troubleshoot the furnace pilot.

Question
Furnace won't light
My Carrier 58MXA060 won't light. The gooseneck came off of the intake air pipe and allowed water to pool up in the combustion air fan. When I turned the furnace on, the CAF ran for awhile, got hot, and then quit. I drained the water out of the fan but it still will not start. I checked the power to the fan on start-up but can get no voltage. I suspect the circuit board may have failed but not sure. Any help is appreciated

Follow-up
As it turned out, the problem was water in the line to the pressure switch. The condensate drain line was plugged and water backed up causing the pressure switch to stay in a closed position. I unplugged the drain line, disconnected all relative hoses and drained them, and tapped on the pressure switch to let any residual water drain out. That took care of the problem, the CAF took right off, the burner lit, all systems are go.

Question
I have an Interterm electric furnace that refuses to shutdown after completing the heating cycle. It does this intermittently, not all the time. I had a HVAC guy look at it 4 weeks ago, for 15 minutes and charged me 60.00 and did nothing. He said he would need to come back several times and replace one thing at a time and see what remedied the problem. I said no way. I ordered a new thermostat and replaced it myself. Furnace worked okay for 3 weeks, now it's back to working okay for part of the day then blower runs and heats without stopping. Turning the thermostat to off does not cut it off. I'm old and live alone, with limited income. What is the problem, so I can get someone reliable to maybe repair this?

Answer
One of the heat sequencers is intermittently sticking. In defense of the tech he has to see it when it is sticking in order to know which one. May need to leave it running, when that happens, get someone down quickly to see it.
Most likely you have two sequencers, bite the bullet and replace them both. It’s a common problem on electric units.

Bryant Troubleshooting Guide

Troubleshooting of 80% and 90%+ Efficiency Furnaces

Furnace Blower

01. DIY Blower Wheel Replacement
02. Damaged Blower Shaft
03. American Standard Blower Wheel Replacement Part 1
04. Blower Wheels Part 2
05. HVAC Blower Wheel Adjustment
06. Dirty Blower Motor
07. Anatomy a Blower Motor: Replacement
08. HVAC Noisy Blower
09. HVAC 90%+ Heat Problem
10. HVAC Bad Gas Valve
11. HVAC another Easy One
12. Jerry Kelly HVAC Advises: Change Your Furnace's Air Filter
13. How to Change Your Furnace Filter
14. Measuring Month Old HVAC Air Filter Data
15. Wall Furnaces
16. Single-Stage vs. Two-Stage Gas Burners
17. HVAC Fixing an Intermittent Blower Relay
18. The Squirrel Cage Fan. How the Air Flow Works.
19. The Why of the Amp Draw of Furnace Blowers. Their Use in Air Handlers and Furnaces
20. Blower and Heat Exchanger Cleaning
21. How to Change the Fan motor Speed on a Gas Furnace

Gas Furnace Temperature Controls 

1. Gas furnace temperature controls
2. Heat exchanger failure diagnosis, Goodman GMP model
3. How does the gas furnace flame rod work
4. Gas furnace won't stay lit. Cleaning the flame rod
5. Troubleshooting the limit switch on the 80% AFUE gas furnace
6. Gas furnace rollout switch operation
7. How to check the flame rod on the Snyder General GUA furnace

Igniters and Pilots

8. Gas furnace spark ignition controls
9. 58SS and 58GP carrier pilot dropout
10. Carrier 58SS 58GP 3 wire pilot assembly operation
11. 58SS pilot assembly description
12. How the hot stick ignitor works on the gas furnace
13. No heat, troubleshoot the HSI on the Snyder General GUA furnace.
Gas Valve
14. How to test the gas valve on a gas furnace with an ohmmeter
15. A look at the GSI electronic manometer
16. How to check gas input pressure on the RGDA furnace
17. Gas valve troubleshoot, Snyder General GUA furnace
Gas Burners
18. Gas burner types
19. Gas furnace manifold orifice sizes and flow rates

Pressure Switch

20. Troubleshoot the pressure switch on the 80% AFUE gas furnace
21. Diagnosing pressure switch problems on gas furnaces
22. How gas furnace pressure switches work
23. How to test water column gauges for gas furnaces

Transformer