How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Phil Your Own Question
Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
23932409
Type Your HVAC Question Here...
Phil is online now
A new question is answered every 9 seconds

Carrier Furnace fan keep running at very high speed. Once

Customer Question

Carrier Furnace fan keep running at very high speed. Once power is on, can hear 2 clicks on the furnace control, and then the fan will start blowing at very hight speed nonstop. Disconnecting the thermostat R wire from the control board will stop the fan. Unit is working properly when heat or cool is called. Already replaced the limit switch, and control board. Model 58uhv.
Submitted: 5 months ago.
Category: HVAC
Expert:  gotoman for ac replied 5 months ago.

What is model number of furnace please. Russ

Customer: replied 5 months ago.
WEATHERMAKER® 8000VS VARIABLE SPEED – 58UHV
Expert:  gotoman for ac replied 5 months ago.

Move red on your board that has gas temp rise to middle and try furnace to see if is blowing warmer air. Russ

Customer: replied 5 months ago.
Russ, I am currently not at home. I can try it when I get home.
I don't get what you mean by "Move red on your board"?
Customer: replied 5 months ago.
Russ, both heating and cooling are working fine. when heat or cool is called, the fan is running at slow speed, and is blowing warm or cool air. but once the heat cycle ended, fan resumes high speed nonstop.
Expert:  gotoman for ac replied 5 months ago.

This problem will be in board or fan module. This something you cannot check yourself. Needs special instruments to check. You will need to get a technician. There is only so far we can go. Russ

Customer: replied 5 months ago.
I already replaced with a new board, and the problem continues. Also, If I disconnect the TStat R wire from the board terminal, the fan also stops. so I suspect it is more a shorted wires of maybe Y or Y2 or G?
Expert:  gotoman for ac replied 5 months ago.

You can remove one wire at a time and see when fan stops. Start with Y2 because that is high speed. Russ

Customer: replied 5 months ago.
I will report back when I try it later at home.
Expert:  gotoman for ac replied 5 months ago.

The G terminal causes fan to run at 50% speed. Just let me know. Russ

Customer: replied 5 months ago.
I think the fan is running at 100% or higher nonstop. it is very strong compare to when it is in heating mode. what would cause the fan to run at this high speed?
Expert:  gotoman for ac replied 5 months ago.

That is ECM. Electronic Communicating Motor. The board communicates with module to tell motor the correct RPM. In my Experience it is the motor module that causes the problem. The symptoms are when thermostat is satisfied the motor takes of to high speed or higher. More or less runs away. Russ

Customer: replied 5 months ago.
I see. is there a way to test the motor module?
Expert:  gotoman for ac replied 5 months ago.

Look at motor and unplug the connector that has the most wires. This goes from fan board. Reinstall and try fan to see if it works ok. Russ

Customer: replied 5 months ago.
I am lost on the "Reinstall" part. do you mean to "plug the connector" back?
Expert:  gotoman for ac replied 5 months ago.

Yes

Customer: replied 5 months ago.
ok, will report back.
Expert:  gotoman for ac replied 5 months ago.

Will be here. Russ

Customer: replied 5 months ago.
Russ,
after disconnecting y/y2 from the control box terminal. all is fine for heat. fan no longer keeps running. it stops in about a minute after heating cycle. So I measure the ac voltage of the 2 blue wires at y/y2, one is 4 volt, one is 24 volt. what can I check next?
Expert:  gotoman for ac replied 5 months ago.

Darn good troubleshooting. Sounds like there is a short between R and Y2. Put wires back on terminals at Y2. Disconnect Y2 at thermostat and see if the fan runs normal. If it runs normal problem is thermostat. If not shorted wires. Check this and get back with me. Russ

Expert:  gotoman for ac replied 5 months ago.

At least heat is running normal now. I will be in and out. I have a Bryant dealership. So I will be out checking techs and bidding jobs but I will check in. Russ

Customer: replied 5 months ago.
Russ, thanks. will do and report back.
Expert:  gotoman for ac replied 5 months ago.

I will be waiting.

Expert:  gotoman for ac replied 5 months ago.

How is it working. Russ