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Joseph, HVAC Technician
Category: HVAC
Satisfied Customers: 97
Experience:  38 years diversified HVAC/R experience,Presenty an HVAC/R Contractor
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I have a Trane 2TTB3048A1000AA central air unit. Yesterday

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I have a Trane 2TTB3048A1000AA central air unit. Yesterday it seemed to not be working..However I have3 units and I noticed this unit the fan was running in reverse and blowing the air down into the unit instead of blowing it out. about a month ago a service changed the capacitor. All was fine until yesterday. now when the outdoor temp cooled the until began cooling the house again.

I find it strange the fan works but out of the blue starts running in reverse

Joseph :

If this system is an older unit, and it's the original motor chances are your motor is on the way out. Hopefully the service tech. installed the correct size capacitor last month. What was the reason for the service call last month. If same problem, I would consider replacing before it stops. If your mechanically inclined you can change out yourself. Get a OEM motor, so the wiring hookup is the same and get a new matching capacitor.


Should I order a capacitor and change 1st before changing the motor. Is it normal for a fan to just all of a sudden start running in reverse?


the unit was installed in 2006 when house was built

Capacitors are not expensive, you would need to find out if you have a three terminal or a two terminal capacitor. A three terminal capacitor has hookups for the compressor and fan motor A two terminal cap. hooks up to the fan motor only. So located the run capacitor and find the MFD rating on the cap. It will state on the side something like 35/5 370 volt or 440 volt the 35 Microfared is for the compressor the 5 MFD is for the fan motor hookup. Motors worst enemy is heat, your internal motor windings may be breaking down due to heat, dirt, uneven voltage over the years.

Customer: replied 4 years ago.

I have this info.. It is a 3 terminal.

Have you ever experienced a fan running in reverse on its own?

If you have did changing the capacitor correct the direction of the fan

In the 38 years in this profession, yes I have . Not a real common service call ,but yes I have. If the motor is turning backwards when the A/C is not running you have a shorted motor, your picking up 115 volt to ground , it may also turn more slowly than normal if it's shorted to ground.
Customer: replied 4 years ago.

Fan only turns when unit cycles on. I will replace capacitor see if it corrects. If not I will replace motor

Changing the capacitor is the most economical way to go, remember if you still have problems and buy a new motor, don't automatically think that the new capacitor your going to buy will match the new motor. If your handy with a ohm meter check the motor for ground .One lead on the metal body other lead on each motor leads .You should not get a reading .
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