P-66 or motor

[hands]

I need so help. Had call on a Trane Condensing Unit, M# TTA120B400EA with a low ambient kit. P-66 fan speed control and Hot gas bypass. The fan motor bearings were bad. Got a new motor and capacitor, installed them, started the unit and the fan motor would not run and the compressors tripped on high pressure. I jumped L1 to M1 on the P-66 and the motor ran at full speed. At first thought, you would say the P-66 is bad, but I remember about 3 years ago the same thing happened on another unit and another guy looked at it and said it was a bad motor. I think he said the windings were shorted together which caused the motor not to run through the P-66 unless it was jumped. It had happened to him before. We changed the motor and it worked fine. I just can't remember how he checked it. I ohmed the windings and had 13.1, 14.8 & 14.0. Has anyone had this happen to them and if so, how did you check the motor and P-66.

[Jpaulsmith]

I may be mistaking but doesn't the P-66 act like a VFD in that it lowers and raises voltage to the fan to control the speed? If so is your motor rated for that. Have you made sure your P-66 is sensing the correct pressure.

[OhioTech]

All electric aside...make sure you are using a ball bearing motor. A sleave bearing will fail.

[hands]

This motor is the third one from Trane. The first one that was ordered was for the standard unit, not one with a Low Ambient Kit. I brought in the bad motor and they ordered another one from the numbers on it. This one was the wrong frame, nothing like the bad one. The third motor they ordered, the one I installed, is one that comes with the Low Ambient Kit, so I'm told. And yes it is a ball bearing motor. By the time I got it installed, it was the end of the day and starting to rain. I didn't check to see if I had voltage on M1 of the P-66 when I started it, the unit went off on high pressure before I could get the cover off of the P-66. Like I said before, the motor would run when I jumped L1 to M1. I will work on it in the morning. The unit I had the same problem with three years ago, I think it had voltage on M1 but the motor wouldn't run.

[GoColts]

I may be mistaking but doesn't the P-66 act like a VFD in that it lowers and raises voltage to the fan to control the speed? If so is your motor rated for that. Have you made sure your P-66 is sensing the correct pressure.

You are correct, if I remember correctly there are 3 different pressure ranges that they operate in. For example the ones I use are 185-245 psi range. So at 185 psi the motor is at 3% then at 245 psi the motor is at 97%. The P66 shortens the life of the motor big time, 3 years is the most I have ever seen one last.

[james mo]

Is the 24vac control voltage present?

[hands]

Went back today and put my gauges on ckt 1 and had around 20 psi on suction and 50 psi on discharge. This was with the unit off. This C.U. is the 1st and 2nd stages of cooling. Another 10 ton C.U., without Low Ambient kit, is the 3rd and 4th stages and the evaporator was a block of ice. The unit I replaced the motor on has the P-66 on ckt 1 only. So when I first started the unit yesterday comp 1 went off on low pressure while ckt 2 went off on high pressure. I thawed out the evaporator and started the unit. The fan started when the pressure got around 190 psi. Checked the charge on all four ckts and they were good.

[Jpaulsmith]

Sounds like your problem isn't with the p-66 or the motor.