Air conditioner wont condition air :(

[Air21]

Howdy, hopefully I'm in the right place.

So I noticed my AC stopped pushing cold air and went out to investigate. Its an older Miller condenser outside the house and I had never poked around it before. With power to the unit and the thermostat set to "Cool" I could hear the audible click of the relay but neither the fan nor the compressor would run. Removing the panel it was obvious the starter capacitor had taken a dump, and probably had been dying for a while, two of the wires had visible burn damage from touching the capacitor housing.

My buddy brought me a new capacitor and we got it installed. Pushed the test button on the relay and everything came on, set the thermostat to cool and it ran cool... for a while. I went out to investigate and noticed the same sound from the relay, it clicked at a constant interval which I assumed was in response to the thermostat. With the thermostat off there is no click. With power to the unit I can push the relay test button and the compressor and fan both come on. I also replaced the damaged wires.

The relay was pretty cruddy looking as well though it showed no visible damage but seemed to be sticking in its position. My buddy had a new relay in his truck so we replaced that as well. Now there is a new relay, new capacitor, and all the visibly damaged wires are replaced.

Same symptoms though. With power to the unit I can push the test button, everything comes on, fan and compressor. With the thermostat set to cool I hear the audible click in the relay, but nothing comes on.

My HVAC buddy is out of town for the weekend, and I'm a machinist

Any ideas guys?

 

[LS6 Tommy]

Manual hi or low pressure switch? Pics of controls? I don't follow the "Test" button thing. Never heard of Miller before! So maybe it's specific to that brand.

Tommy

 

[bonneyman]

Miller used to be IIRC a mobile home brand. One of the big 3 back in the day for mobiles. Coleman, Intertherm, and Miller.

Pushing a reset button sounds like the high pressure trip switch. Could be an overheating cond fan motor.

 

[Rookie2]

Did you try pushing your "test button" with the thermostat set to cool ? If it stays on then you may have a bad connection or low 24vac.

 

[Air21]

I assume it's a test button, the relay has a button on it, if you push it then it closes (opens?) the relay and everything runs, when you release it stops. The button doesn't move in normal operation. The relay is a MARS 91311.

Pushing the test button with the thermostat set to cool only works the test function. In fact if you are holding it in when the thermostat signal comes you can feel the solenoid clicking inside the housing, but if you release the button it does not stay running.


SOMETIMES it all comes on and runs cool, but most of the time the relay just clicks as it receives the thermostat signal. It's a real ***** when I try to run it over night because it will cool for maybe an hour, and a few hours after that the lack of circulation and the 86 degree overnight temperature makes it kinda uncomfortable.

I'll try and get some pics.

 

[Rookie2]

Never seen a contactor with a test button. Could be thermostat,circuit board or wiring.

start by cutting off the wire nuts on the incoming thermostat wires and rewiring them with clean connections. then go inside and clean/tighten thermostat wires on the circuit board. Turn off power first !

 

[zmaxmotorsports]

How about a picture?

 

[Air21]

Relay and I'm pointing at the "test button"

Here is the whole shooting match...

 

[Brian_WK]

Check for 24 v going into the circuit board at the yellow wire nuts, out of the circuit board at the red and black terminals, and at the 24v leads going into the contactor. I'm guessing it is that circuit board which is probably a time delay, un-needed if you have a modern digital thermostat.

Brian

 

[bonneyman]

Oh, circuit board! Probably just a time delay board. Doesn't look like a Heat Pump/defrost board.

Bypass the board with power turned off and see if it comes on when the power is restored. Board might be fried from being out in the heat and not closing. And if you have a electronic/programmable t-stat, it has a compressor time delay built into it - you don't need this timer board.

 

[LS6 Tommy]

Everyone pretty much covered the time delay issue. That "relay with a 'test' button" is the contactor. It's not a test button. That just indicates whether the contactor is "open" (sticking up or flush with the surface) or "closed" (pulled in).

You also should put fork or ring connectors on the compressor wires where they go on the contactor.

Tomy

 

[Air21]

So delete the board in the bottom left. And connect black to black and red to yellow. I'm on it!

You guys are Awesome, I don't care what they say about you in General Tool Discussion . Thanks!