Contactor Sticks and can't find exact replacement

Old 06-23-18, 12:23 PM
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Contactor Sticks and can't find exact replacement

Hi All,

I am struggling to find a direct contactor replacement that is on a Trane 1984 Central Air Unit. I have serial number and model BTD724A100X0
Anytime I order one online they come back way different. I have a few with highlighted examples of new vs old contactor. Any ideas....

SPECS for contactor on the unit right now.
Pole 1
LRA 18
Pole 2
LRA 90
FLA 18

The item I was recommended and purchased Model 5MMA7
240V and all its says is

Process**** I have put in the new contactor and it fails to turn the unit on outside. I matched up each of the wires and then traced the thermost wires to the ac and noticed there is a sodder stem on the terminals.

I matched up the location on each side and nothing. When I manually push the contactor down everything works compressor etc. I have switched up the themro wire combination and nothing works. I thought maybe i shorted things out but I replaced the new contact with the old one that was on there and everthing works like a just sticks every so often because its old. Any ideas? Please see pics the ONLY thing different from the old vs new is one of the upper terminals has a post where are the new one has a flat metal screw hole. I belive amps and switch is same.

Any ideas would be greatly appreciated...
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Old 06-23-18, 03:51 PM
Bob14525's Avatar
Join Date: Jun 2013
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It appears that the 5MMA7 contactor has a 240V coil. Most US A/C systems use a 24V coil. When your thermostat calls for cooling, it sends 24VAC to the contactor coil. This causes the contactor contacts to pull down, turning on the outside unit. However, since the contactor you purchased has a 240V coil, it requires 240V rather than 24V to make it turn on. That's why it's not working. Purchase a contactor with a 24V coil and it will likely work fine.
Old 06-23-18, 04:26 PM
Join Date: Jun 2012
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The equivalent 24v would be 5MMA5

Most would just use a generic 24v 30a contactor but generic has different connects that you have to deal with.
Old 06-28-18, 05:04 AM
Geochurchi's Avatar
Join Date: Nov 2012
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Hi, can you post a pic of the wiring schematic, itís a bit hard to see the connections on the contractor ,as mentioned a standard 30 Amp 2 pole contractor with a 24 VAC coil would work.

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