trane RTU keeps failing

[snowbird225]

I have a unit that I cannot find an issue with. Pressures are good, coils are clean but the unit fails over night. Belt was super tight and had black dust on the pully so I changed the belt and check the bearings. Everthing looks good. The tstat keeps reading cool fail when I return but I can never find a problem and the unit runs great all day. Been going on for a few days. Can anyone take a stab at this.

[timebuilder]

Trane stat, or a conventional stat using the interface board?

[OldSchoolMech]

How cold does it get at Night Below 55? If the temp drops low over night it could be failing cause its not desgined to work in those conditions unless the proper controls where added.

"Take the batteries out shake them and blow on them. Place them back in and that should do it"

[snowbird225]

It is a trane tstat. And the temp at night is about 85 degrees. During the day temp gets to about 95 or so.

[timebuilder]

It is a trane tstat. And the temp at night is about 85 degrees. During the day temp gets to about 95 or so.

Are you saying that the SETPOINT is 85° overnight? What is the overnight ambient temperature?

[snowbird225]

No the set point is 72. The ambient temp is 85 at night and 95 during the day.

[jrmech]

the unit fails at night and it starts working in the morning by itself, or do you go out and reset at the disconnect?

check t-stat programming, change the battery...

what are the pressures at 95F?

not much to work with here, more info needed.

[snowbird225]

Yes, I go out in the morning and when I get there it is out on cool fail. So i reset the unit after I look for faults. I was running an 80 psi suction and 255 on the head. (R22) I watched the unit cycle on and off and the tstat seems to be operating great. I pm'ed the other units and kept coming back to check this one and it was running good. suction line sweating and temp in the conditioned space was 72 just as it was calling for it to be.

[snowbird225]

Could the economiser do this

[AddMore22]

Is it on any type of control system ?

[snowbird225]

No just a trane tstat

[iceman35]

Are there any codes on the UCP board? I had a trane rtu that never gave me any alarms. The whole time the board was showing normal operation, condensor fan motor was the problem. it was tripping on internal overlaod after a few hours of running, also you may want to disable the economizer.

[jrmech]

check for power at y1/2 in the morning...if its there than check where control voltage is being held up.

are there multiple units for this customer or are you on a plaza roof of some kind?

[snowbird225]

Shows normal operation on the board. I'll try to disable the economiser. I just don't see why it works all day and not at night. I take that back I did check the board on the economiser and it showed co2 sensor but not the last time. Where would that sensor be at?

[snowbird225]

It is a walgreens.

[btack]

Heres a guess. There is an occupied switch, relay, out something to that effect that when energized cuts the blower out. This cause low pressure and or freeze stat. Maybe a timer something that breaks "g" or maybe the blower contractor since it it's a a trane unit and don't want to use normal terminal designations
Sent from my amazing 4G device

[DNMechanical]

check superheat and subcool. only pressure not good enough

[snowbird225]

Another tech went out this morning and eventually found that the condensor fan motor was pulling to many amps. He found the compacitor to be bad. I guess we will find out in the am if that was all it was. Thanks for all of the feed back guys.

[AddMore22]

Huh .... Odd that it would lock out at night due to high amp draw on cond fan.

[snowbird225]

I thought the same thing. We will find out tomorrow. I have feeling I'll be back out there.