RTAA power loss fault.

[Randy S.]

I have an RTAA that has locked out compr. A several times on power loss fault, first about two months ago, and I tracked all the wiring down and finally just cleaned out the aux contacts on the main contact with some contact cleaner, and it ran fine until this last weekend. Many cycles on and off with no problem. No transition faults.

Now I have a call-back on the same fault. No transition faults, just the goofy power loss lockout of the circuit.

I'm a centrifugal guy, mainly. Am I barking up the wrong tree here?

[maxster]

pull each CT off the board... ohm it out,and check how tight it re-pins(bend the male pin on the board slightly),also check the CT where it is mounted onto the T side of the contactor.those wire ties are installed tight from the factory.write down the CT ohms as yo go they should all be in range of each other.just a bound on that pin/worn CT will reflect to the UCP that there is a power loss from the 3 phase comming in.while you repinning do any and all pins/boots just that you know you did that.

[scott123]

Is this a "phase loss" or a "power loss"?

[Randy S.]

Power loss is the fault I get on the display. Only on the one compressor.

Going to the site this morning.

Thanks for the info.

[scott123]

You need to check the transistion complete input. replace the aux contact first and see if the issue goes away. A power loss diagnostic means the UCP lost power on all 3 legs. Also make sure the interlock for the starter is good. I will do a little research today and get back to you. I assume this is Y-delta?

[orland25]

Check the Board contactor" maybe loose weld"

[Randy S.]

Checked the CT's, tracked down the CT and starter wiring back to the boards, tweaked the pins a bit so they are tighter in the plug, checked aux contacts again, and restarted the unit.

The plugs did feel loose to me.

[maxster]

where your CT ohm readings in range of the others at the boots

[scott123]

Originally posted by maxster
where your CT ohm readings in range of the others at the boots

A "power loss" diagnostic involves all 3 legs. Therefore a differential reading between each CT (if present) would not generate a "power loss" diagnostic. More likely you would see a "severe phase imballance".

[jimbob73]

When you check the auxillary contacts for transition complete signal, Do so with meter set to ac voltage and check across transiton complete aux contacts on startup. I have seen many times now where it checks out ok with an ohm meter when pushing the contactor in with power off. But put 120 to it and it will not pass thru with aux. pulled in.

[Randy S.]

I'm suspicious of the NO contact on the main contactor.
So, contrary to my nature, I'm going to throw a part at it.

Not one transition fault.

[scott123]

A power loss diagnostic is different from transistion incomplete. Transistion incomplete is generated when a failure to recieve a complete signal occurs from the 2K2 aux after a call for transistion.

This same 2K2 aux can also cause a power loss diagnostic. If a transistion complete signal sucessfully occurs, but later opens again, a power loss diagnostic will be generated.

[Randy S.]

I got lucky and was right there when it happened.

It was running along well, and then I heard the contactors chatter a little, and then it sounded like it went back into the Y mode for a couple seconds, and then dropped out totally, with the power loss fault showing on the display.

I changed out the N.O. aux. contact on 1K1, what I commonly refer to as the main line contactor. Probably a little flake of plastic hung up in it sometimes.

Cutler-Hammer "Freedom Series" contactors. I've cussed 'em before...

[justatech]

Have you removed the top cover of the contactor and checked the shade rings on the coil. I have found several contactors an AA's where the laqcuer had come loose and the shade rings had come loose. This will cuase contactors to chatter and have also found contactors locked closed by a loose ring. If this is the problem replace the contactor the rings are pressed on.

[Randy S.]

I didn't have a look at the shading coils. Every other time I've found broken shade coils, there was a constant buzz.

[r404a]

A question, and a statement. First, a question. Maxster what are you refering to when you say "Repinning"? A statement. Jimbob, I believe that transition signal (Aux 3) is DC, 12 volts.


Thanks for the replies.


r404a

[always looking]

Good post! I have moved from out East to desert climate and I have ran into this at least 5 times in a year. It is so dusty out here tha auxillaries have been the problem every time and because of the way they are made cleaning them usually just leads to call backs. They need to be replaced after you determine that cleaning them did help.

[drivewizard]

Good post! I have moved from out East to desert climate and I have ran into this at least 5 times in a year. It is so dusty out here tha auxillaries have been the problem every time and because of the way they are made cleaning them usually just leads to call backs. They need to be replaced after you determine that cleaning them did help.

Try installing a sealed relay with the coil wired parallel to contactor coil. Then run the wires that normally go thru aux contacts thru the relay N.O. contacts.
That may give you more time between failures.

[Randy S.]

The best I can tell was that it had to do with a poor connection where the CT wires land at the board in the good ol' AMP push on pin connector. I slightly tweaked the pins and then worked the connector on and off several times.

That's been like four months ago, and this machine runs 24/7.

Once in a while, something works...:D