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Ask Brian HVAC Guy Your Own Question
Brian HVAC Guy
Brian HVAC Guy, HVAC Technician
Category: HVAC
Satisfied Customers: 846
Experience:  I have been an HVAC/R mechanic/technician for 30+ years.
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Fan not coming on

Customer Question

Fan not coming on
Submitted: 1 year ago.
Category: HVAC
Expert:  Brian HVAC Guy replied 1 year ago.
Hi I'm Brian and I'm here to help! Can you clarify your voltage reading for me please? You say you have 120Vac on black and yellow wire coming into motor. Are those readings to ground or is the reading between the black and yellow wires? Thanks,Brian
Customer: replied 1 year ago.
It's 120 vac on yellow and 120 vac on blk to blower
Customer: replied 1 year ago.
That is to chassis gnd
Customer: replied 1 year ago.
I don't have a tester to measure farad on the capacitor but I can read 120v on each brown wires coming from the blower
Expert:  Brian HVAC Guy replied 1 year ago.
Thanks. This fan-coil is 240Vac unit. You should measure from line to line. If you don't have 240Vac between the black and yellow wires, then your fan relay or fan control board has failed (as long as cooling or fan On is being called for from thermostat). You should have 24Vac from R to G on unit (red and gray low voltage wires). If you have 24 volts between R and G and 240Vac between the Yellow and Black motor wires and the motor is cool, your motor has failed. Let me know what you find and we'll go from here. Thanks,Brian
Customer: replied 1 year ago.
I get no voltage reading between the yellow and blk ,
From the C side of the transformer (going to the fan) and the blk wire coming from the relay control board to the fan
Customer: replied 1 year ago.
I get 24-27 vac betw the R and G on the control board
Customer: replied 1 year ago.
Looks like the fan relay sits on the control board
Expert:  Brian HVAC Guy replied 1 year ago.
Ok thanks! Now we're closing in on it! I misspoke earlier but that tells me a lot! You should have 24 volts nominal between Brown, C,(not Red, R) the low voltage 24 volt common low voltage connection and Gray, G, the fan wire wire connection (green to the thermostat usually). The fact that you have 24 volts between R and G tells me your thermostat is not calling for the fan to run. Jump R to G (essentially bypassing the thermostat) and see if the fan motor runs and let me know what happens. Sorry for the brain fade!
Expert:  Brian HVAC Guy replied 1 year ago.
FYI that is a 24 volt connection at R, C and G so don't worry about it shocking you. It may tingle a little though.
Customer: replied 1 year ago.
When I short R and G, the fan kicks on
Customer: replied 1 year ago.
So Do I have a bad thermostat?
It's a aprilaire 8800
Expert:  Brian HVAC Guy replied 1 year ago.
Ok, you can close up the air handler then, the problem is not in the air handler. I'm not familiar with the Aprilaire 8800, just reading the manual now. It would appear to be an issue with the thermostat but let me read a little further. Does the 8800 control anything else? Is the 8800 networked to some other device(s) or control unit?
Customer: replied 1 year ago.
Yes we have the serial interface at the thermostat connected to an ELAN HC6 automation controller
There three other thermostats connected the same way in the house
Expert:  Brian HVAC Guy replied 1 year ago.
Well, at the thermostat that the unit in question is being operated from, try jumping R to G there. If the fan works there then there could be something wrong in that thermostat or possibly the automation system. I'm not familiar at all with that system so it's probably best for me to opt-out to see if one of the other experts here is familiar with that system.
Customer: replied 1 year ago.
I believe the serial conn runs independently from the Handler
It only sends and receives commands
Let me check shorting at the thermostat
Expert:  Brian HVAC Guy replied 1 year ago.
Very good, meanwhile your question will remain on the board for all experts to review and post if they have anything to add. I'll read more about your system and post back if I can find anything of value or possible further checks. Thanks,Brian