No AC - contactor OUT

Problems related to residential installations.

No AC - contactor OUT

Postby jonzo2245 » Tue Jul 12, 2016 8:28 pm

- Trane XL12 Heat Pump & Trane TWE040E13FB Air Handler
- No cooling & and no inside fans, and no activity at heat pump outside.
RECENT - massive lightning strikes last week?

Outside -
- when I first checked the outside heat pump unit, the capacitor had a burned terminal at the HERM connection, so I did replace the capacitor .
- contactor is OUT
- when i push contactor in, unit starts normally
- top and bottom on right side of contactor reads 240v
- top and bottom on left side shows 0

-
- thermostat on wall shows 24v @ RH + G, and looks fine

Air -
- in basement shows 24v @ RH + G
- when I jumper them together, fan starts up on its slower speed, but nothing else
- both fuses look fine
- light on left side of control board blinking fast
- when I jumpered the RH + G, the control board light on left side would stay on a bit, then go dark, then blink six times, then start the cycle over

Installed new control board, due to the 6 blinks on the green light in it, but all remains exactly the same.

So now, am wondering if I should have replaced the contactor, too, since I had a burned HERM tab on the cap?

Any advice greatly appreciated!!
jonzo2245
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- No AC - contactor OUT

Postby Freon » Wed Jul 13, 2016 9:34 am

I would first determine the condenser contactor's status. Call for AC at the thermostat. At the air handler measure the voltage between the Y and Common terminals where the connection is made with the control wires going to the condenser. You should see 24 volts. If you do see 24 volts, then pull the disconnect on the condenser and measure the voltage where the control wires connect from the air handler connect to the contactor coil. Again you should have 24 volts. If you do, then the contactor seems to be the problem.

If there is not 24 volts between Y and common at the air handler then turn off the air handler power and remove the thermostat cover so you can directly jumper Y and R at the thermostat. If the condenser starts the thermostat is the problem.

If there in no 24 volts at the contactor itself but you have 24 volts at the air handler between Y and common, the control wire may be the problem.
Freon
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- No AC - contactor OUT

Postby jonzo2245 » Wed Jul 13, 2016 4:47 pm

Thanks so much for the response! Can you explain where the "common" terminal is at the contactor? as in -"between the Y and Common terminals" OH...NVM.....you mean the 24v terminals on the sides of the contactor.
jonzo2245
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- No AC - contactor OUT

Postby Freon » Thu Jul 14, 2016 10:18 am

Yes, the 24 volt terminals on the contactor usually close to the base of the coil. If you have the 24 volts at the contactor coil then the coil is bad and you need to replace the contactor.
If you do not have 24 volts at the contactor coil then you work back to the air handler control board measuring the voltage between the Y and C connection points. If you have 24 volts there, then you need to look for a break in the wire from the air handler control board to the contactor in the condenser. My guess is this is not your problem because of the electrical storm.

I think you will find 0 volts between the Y and C terminal at the air handler control board. Since this junction is simple a connection point from the 24 volts coming from the thermostat, I think your thermostat may very well be the problem. Jumping the R and Y terminals at the thermostat (you said you had 24 volts at the thermostat) will tell you if the thermostat is the problem. Always turn off the power to the air handler when removing the thermostat cover exposing the base or adding jumpers. Then reapply power.
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