Need help with indoor AC unit

[tb-av]

I know some here probably know this.....

My indoor Trane AC unit won't stop running unless I turn the main breaker off.

Switches on thermostat make no difference
Outside unit does turn off

Indoor fan runs 100%

When I click the circuit breaker off, within about 2 seconds I can hear a relay release, so I figure the circuit board must be bad. Everything I have read says it must be the fan relay or fan delay relay.

The part number is RLY02257 which has been replaced by RLY02807
http://www.ebay.com/itm/NEW-RLY02807-RLY02257-Time-Delay-Relay-HVAC-Trane-/230531160305

the directions say to replace wire for wire on same number / letter terminal. However my concern is colors( both red) matching up.
If you look at the diagram FIG-3 is what I have.
My connections are
T=Green -- This matches new part
B=Blue -- This matches new part
A=Red -- This matches new part
6= White/J -- This matches new part
3=FAT RED WIRE to FAN -- This is the one I want to be certain about.
4=Blue -- This matches new part
1=Red -- this wire is normal size like all others and I want to be sure it goes to 1(com).

So FAT RED WIRE = 3(NO) and thinner red wire goes to 1(COM)

Thanks for checking my work here.

TB

[nineteenkilo]

Sounds like the contactor is stuck. Look inside for what looks like a set of old-style points out of a distributor, but larger. See if they are arced together. They should not be making contact until voltage is present on one side.

I know this doesn't sound very clear. They're copper contacts with springs.

Should look something like this. http://www.chinacontactor.net/Contactor/MBC-2X-AC-Contactor.jpg


I asume yo uhave a basic multimeter and know how to use it without blowing yourself up? I have to ask for my own peace of mind.

[Suwannee Tim]

Sounds right. You want to confirm the thin red wire is hot AC power. Have your wife hold the bare part of the wire and put her other hand on something grounded like the bare metal of the air handler. Now turn the breaker on. Observe her reaction. If she does nothing it is not hot AC power, get back to me. If she smokes, screams, falls on the floor, etc. you have confirmed the wire is hot. This can also be done with a meter if you have one.

Seriously, don't use your wife or anyone else for a hot AC detector. I would want to confirm the thin red wire is hot AC. You can follow it to a junction or ohm it to a junction or check that it gets hot when you turn the breaker on.

I don't think the old contactor is stuck, I think the time delay electronics have failed and are holding the contactor in. Replacing the contactor is the correct plan.

[tb-av]

Ok, I'll reconnect things and check that thin red wire.

Unfortunately I can't see inside this device. It's all sealed. I would have to drill out rivets that hold the coil and bottom cover plate to the plastic housing.

I still need this one intact in the event I need heat before I get the new one installed which hasn't arrived yet.

Ok, I've just taken a closer look.. Also have the schematic.

POWER SUPPLY = BK RD GR

BK goes to one side of motor/motor start cap and COM of 240/24 transformer.

RD goes to Term 1 of relay and 240V contact on transformer

The thin red wire is actually to a wire nut with another FAT RED wire. It is labeled RED 1 connected to Term 1. Then term 3 is RED 3 and that goes over to the fan motor.

So yes that thin red wire is hot. I can see where it all goes now. I never saw the wire nut with RED 1 before and couldn't understand why there was a thin red wire.

------------
I was going to try to repair the circuit board but there is a lot of surface mount stuff on the back side. Anyway the new part was only $12, I just didn't want to blow it up. I couldn't even repair it with spare parts for that price.

Yes, I'm ok with meters and such but I'm not crazy about 240VAC. I would rather work on a guitar amp with higher voltage than household wires over 120V. I get a little jumpy with 120V sometimes, thinking I have everything turned off only to find wires still hot back in the outlet box.

Thanks for the help. When I get it running again I might drill that old one apart and see if it was the board or the contacts. I also noticed the RED 3 wire to the motor was really loose. I was wiping some dust off it to read the numbers and it just dropped right off. No signs of any arcing there though.

[Suwannee Tim]

Make sure the wire nuts are tight.