Trane outdoor variable speed fan

[drfluke]

I,ve got a 3 ton trane split ac unit with a variable speed fan motor on the condensing unit.I,m Not sure which component is defective. I,ve replaced the outdoor fan thermostat switch which was bad.(sometimes it would close,sometimes it wouldn't.Switch has a close in /out tolerance of 76-80f.Can someone tell me how to check tke fan contol boad (the one with the red led) and the fan motor to be sure I have no problems there. Installed in 1992,model# TTY036A100AO. Any information about this design would be appreciated.To me it seems like a headmaster setup.Could be a servo motor for all I know.I'm green as a gourd and still learning.Thanks, my hat's in my hands.

[airworx]

get a service manual from trane.
i would think that the board is the controller and it senses either pressure or condensing temperture or ambient temperture to put fan on high or low speed. i do not think this is a variable speed motor. so trace out your wiring and see what the sequence of operation is and figure it out.

[2hot2coolme]

Yeah, thats gotta be a 2 stage motor. It measures ambient temperature, high speed kicks in at 85.

[jrbenny]

PWM signal on Yellow wire to motor (wire may be yellow or yellow/brown from control board: 10VDC (+/- 15%) for low speed, 17 VDC (+/- 15%) for high speed.

Works on outdoor temperature as described except it shifts @ 74°F decreasing and 78°F increasing (+/- 5°F both ways).

[drfluke]

Thans guys for your help.Jr sounds like you know this setup well.Yellow wire from stat goes directly to fan control board Y terminal and also to O.D.fan stat switch,which when closed also returns to fan control board.T2 terminal.Output to fan motor comes from A terminal on board via a RD/BK wire.When O.D.fan stat opens,the fan stops completely.I'll check for those voltages on RD/BK wire.What spooked me was when I spin the rotor on this fan motor I Feel magnets{high voltage disconnected} and wasn't sure what I had a hold of here.From your info I'm prbably going to find a bad fan cotrol board too. Thanks for your help everyone!