FAQs on HVAC Blower Diagnosis & Fan Test


How do you know if your HVAC blower isn’t functioning properly?

The HVAC blower fan is known as the heart of the HVAC system. They are quiet and work effortlessly throughout the years to keep your home comfortable. They don’t require a ton of maintenance, but they should be serviced once in a while to make sure it’s in tip-top shape. If you don’t do this, the cost can be mind-blowing.

If you think that your fan isn’t working as it should, it’s probably because it won’t start or you just don’t feel as comfortable as you should in your home. Your air conditioner and furnace will not run as smoothly and those who have experience in the field will know that the obvious issue is the fan. They may know this because the motor won’t turn on or makes a lot of noise.

If it comes down to it, you may need to invest in a new blower. You or a professional must test your equipment over time. They will know exactly what to look for and they will run a series of tests to make sure that everything is operating as it should. If it’s not, they may fix it for you.

Here are some common FAQ’s on fixing the air handler fan

Q: I have a common air conditioning unit that runs very well but I noticed that when the compressor starts it gain more load on power. And it also stops the compressor for once. So I check the compressor and found that the blower runs slow rotation. After that, it stops. I checked and confirmed that the power voltage is normal. As it could not start, on and off repeatedly, without tripping any breaker or fuses. What is the cause? The blower motor only gets hot without running.?

A: There might be an issue with the compressor or perhaps the fan motor start/run capacitor. Or at this point, the blower motor could be seized. I’d leave the device switched off to prevent the chances of an electrical fire. If your compressor fan and/or air handler unit fan works slowly try to find low voltage issues, a bad run capacitor, or perhaps failed bearing that’s seizing.

Q: If the temperature on the thermostat reaches 85-86 my blower will begin by itself. Once this occurs I can’t start the compressor till the blower shuts off. We must switch on the air before it gets to 85-86 to ensure the device to run properly. Any ideas?

A: May appear to be a bad control board

Q: I have a heat pump system. When the thermostat is in the heating position, the HVAC blower fan continues to run after the desired temp is reached and the outside heat pump unit stops. The thermostat will continue to show heat1 in the process after the heat pump has stopped and the temp has been reached.

When I reduce the temp on the thermostat the fan will stop. I have removed the wire from the thermostat at the control board and the fan continues to run after the desired temp is reached and outside unit is off. I have turned the power off at the air handling unit for a reset and the system will function as normal. Later on, it will return to the same problem. I have a feeling the control board is not functioning as desired.

A: Check to see if the backup heat is operating.

I meant to suggest that if you continue to receive heat from the system and the blower fan is thus operating after the outside compressor condenser has turned off then you are probably running in backup heat mode.

In heat mode, if the heat pump can’t offer heat the backup or aux heat has to work, else you’ll get no heat but the blower may run – depending on-unit controls.

If the blower fan runs on after the thermostat is satisfied, blowing cooler air. A brief heat extraction run-on is normal, typically a minute or less. Many minutes of running-on points to a bad fan limit switch control.

Use the search box above to search in our article series FAN LIMIT SWITCH to see locations and appearance.

Air Handlers that use gas or oil-fired heat source would use a fan limit control switch. An Electric heating system used as a backup for heat pump would not need that control. If that’s your situation then I suspect there is a corroded electrical connection or a bad control board or relay in your air handler.

Q: In my carrier weather maker 58. The blower isn’t coming on when t-stat is set in auto. A/C comp. It starts up but no fan. Same with heat. Everything starts up normally except no blower. I switch t-stat to fanon and blower works along with a/c comp.

And the system works normally except fan doesn’t cycle because it’s in a fan on mode. The control module was smoked after a nearby lightning strike and has been replaced. I think it’s the blower control module but before I install I’d like to find a way to prove that’s it.

A: Common causes a bad control board. If it were the relay the fan wouldn’t run on manual on

Q: I have a carrier split unit 2011 year model heat pump. The blower stopped working on the indoor unit after a lightning storm. I replaced the module for the motor which is the x13 model. The module has the capacitor and everything built into it.

After replacing just the module end of the motor the blower came right on and runs perfectly except now it will not shut off unless I open the breaker. The control switch is in auto and the control is in off, yet the fan continues to run.

I swapped thermostats with the downstairs unit and still have the same problem. I bought new relays and replaced and still have the same problem. I then bought new thermostat wiring and still have the problem.

I also swapped out the control board with a unit from downstairs and still have the continuous running blower. The outside part of the unit runs fine and cycles on and off by the temp as it should.
A: Did you remember to check that there is no manual on switch on the fan limit control itself? Sounds like a stuck fan relay or shorted wires to the relay; I’d start by disconnecting the wires from the thermostat on the air handler end.

Q: Condensation dripping into the bottom of the return behind the filter. Drips straight down off coils, never makes it to the drip pan. Soaked up more than 4 cups of water. Professionals have cleaned coils twice. I did not make any difference. The unit seems to be operating properly. Very cool.
A: Ask your professionals to check the fan speed, air movement speed, against the AC unit’s specifications. You may be seeing excessive condensate blow-off.

Q: My blower works to circulate air or when the “fan” setting is on but shuts off when the A/C unit starts.

A: Sounds like a control board or thermostat wiring problem. If the problem is new your tech will perhaps check the blower control board and relay.

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