Reply to Thread

Got rid of the 50va transformer I installed. Took the original coil wires that came from the control board and put them on the coil wires of a rib relay.(A RIB relay will pull in at 10 to 30 VAC/VDC). ran 24v from the original 75VA transformer to N.O. contacts of the rib relay.

Sent from my SM-G960U using Tapatalk

which way did you solve it, transformer or relay and a 208 coil

Originally Posted by Cool breeze 38

that is a 50va transformer? sounds like its not big enough. going by your spec sheet it needs 32 va to hold it, which is the 1.1 amps. but needs much much more to pull it in. what was the original transformer size.

you could put a rib relay and a 208 v coil. it would fix it. take the current contactor coil leads and put them to the rib coils. then 208v coil on the contactor

You win

Sent from my SM-G960U using Tapatalk

Talked to Trane tech support told me to run my 24v thru a relay which I had already done. He said the UPC may be at fault and has had this same call multiple times in the last few weeks. When I installed the relay I fed the N.O. contacts with it's own 50VA transformer, apparently a 50VA is not big enough to pull in the contactor. I put the 24v side directly to the coil and it would not pull in. Yes the OEM transformers are 75VA but they feed multiple contactors along with the damper actuators. I did wire the same transformer and contactor to 120v at my home and it pulled in no problem. I left the relay in place and ran a wire off the secondary to the relay contacts. The relay coil is energized by the original coil wires. If I get a call back they will be getting a contactor with a 208v coil and a new board.

Sent from my SM-G960U using Tapatalk

Sounds like a safety to me or some sort of loose/intermittent connection.

Can you clip an alligator clip to the wires and run them to your meter and see what the voltage is as it's happening? Could be a voltage drop just big enough to cause it to drop.

When does it happen? As soon as the comp starts or after a couple of minutes and pressure builds up?

Originally Posted by Spitz

Does the snubber prevent arcing in the low voltage relay? Not overly familiar

Sent from my SM-G960U using Tapatalk

Yes.

If you think back to the Kettering (breaker point) ignition systems, the capacitor (called a "condenser" in old radio lingo) was used to extend the life of the point contacts by reducing arcing during the hundreds of thousands of operations, until the points were replaced at the next "tune up."

One key point when working with the Trane snubber circuit is the fact that a high impedance multimeter will allow you to measure a voltage at the circuit outputs when no load (contactor) is connected to the leads because of the ability of the snubber to pass a trickle of current even when the outputs are de-energized, which is more than enough to power a meter with an 11 meg input impedance.

A connected load like a contactor shunts that trickle current, so you will read zero volts across the de-energized coil terminals.

Does the snubber prevent arcing in the low voltage relay? Not overly familiar

Sent from my SM-G960U using Tapatalk

It will have a snubber.

This is a trane, is the output of the board a snubber circuit?

I had a airflow pressure switch kick my tail once but it caused a cool fail not a chattering contactor.

While the contactor is trying to pull in, find the voltage drop in the circuit that is causing the loss of voltage. If you are using a stat call, it could be in the stat or the wiring. Start by disconnecting the stat wiring and make a jumper call in the unit.If you are not using a CTI board, put it in test mode.

You will find a voltage drop. Somewhere.

Originally Posted by Spitz

I dont have a problem taking pressure switches a out of the circuit for troubleshooting.

Sent from my SM-G960U using Tapatalk

Don’t run it long and don’t leave it that way.

I dont have a problem taking pressure switches a out of the circuit for troubleshooting.

Sent from my SM-G960U using Tapatalk

Originally Posted by Snapperhead

Bypass all of the safety sensors ....

Hmmm

It just seems kind if weird, I isolated that contactor with it's own transformer and put the original coil wires on to a RIB relay. I think those RIB coils will pull in at around 10volts. And it did the exact same thing. While the contactor was chattering away I manual pushed it in and it held. very possible the relay could have been chattering also caused by a safty switch but a didn't see it and would think it would be less likely.

Sent from my SM-G960U using Tapatalk

Bypass all of the safety sensors .... see if that fixes the pulling in

A contactor coil is like a motor high amperage until its pulled in. This is what's causing the chattering that high amperage across bad contacts drops the voltage, the coil releases and immediately re-energizes.

Pull the load side of the contactor to prevent pitting the points as you trouble shoot!

Makes sense maybe the new contactor coil draws a little more. I should have just replaced those junk encapsulated switches during the compressor replacement. Maybe put in a real switch.

Sent from my SM-G960U using Tapatalk

Follow the low voltage and test each and every safety switch, one or more are not making good contact under load.

Originally Posted by 71CHOPS

if it worked fine for 25 years, as designed, I would be looking at the path from Y1 to the contactor coil. I have also had pressure switches pass voltage but not enough current, due to burnt internal contacts. all of the times it has happened to me have been on units with issues that caused the switches to cycle a lot.

That's what we were originally thinking but the breaker on the transformer had never tripped before the new contactor went in.

Sent from my SM-G960U using Tapatalk