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airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 8374
Experience:  Furnace, A/C and heat pump specialist.
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Customer Question

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Submitted: 1 year ago.
Category: HVAC
Customer: replied 1 year ago.
I have a Carrier split air conditioning system (no heat pump). The fan in the air handler stopped working. I jumped the green and red wire from the thermostat and the fan did not start up.I took out the fan and tested the capacitor mounted on the motor. The fan has a dual shaft and in a squirrel cage. The motor has an oval 5 MFD at 370V capacitor. The rating is plus or minus 5%. I tested the capacitor and got a reading of 3.6MFD. Should the motor still run if the capacitor is at 3.6MFD ?How do I confirm the voltage going to the motor? I would like to test the voltage going to the fan motor. The fan motor has 3 wires (High, Low, and Line).To test the voltage going to the motor do I simply do the following:Set the thermostat to call for Cool and set the fan switch on “ON”
set my voltage meter to “High Voltage AC”
place one lead form the meter on the LINE wire and should the other lead from the meter be placed on the metal chassis of the air handler? Is this how it is tested?What voltage reading should I get?The model number of the fan motor is Fasco D258
Customer: replied 1 year ago.
The rating is plus or minus 10% not 5% on the 5 MFD at 370V capacitor.
Expert:  airheatman replied 1 year ago.

1. 3.6 is weak, We should get at least 4.75 on the cap.

2. You are correct. One lead to Line and one lead to speed wire. we should get 208-240 volts AC

Customer: replied 1 year ago.
I tested one lead to Line and one lead to speed wire I am not getting any reading. I tested the electrical connection on the main lines that enter the handler housing, I am getting 240volts. Some were between there and the leads is probably the problem. Can it be the transformer. When I turn on the AC on the thermostat the contactors engage on the condensing unit (compressor and condensing fan come on). Can the problem be the fan relay?
Expert:  airheatman replied 1 year ago.

Yes, do you have the model on the unit handy?

Customer: replied 1 year ago.
Customer: replied 1 year ago.
all the high limit switches are closed
Expert:  airheatman replied 1 year ago.

That is model on outdoor.What is model on air handler where fan doesn't work?