AC question, what's the circuit board in the compressor cabinet?

AC question, what's the little circuit board in the compressor cabinet?

My friend's AC is a Lennox HS26-311-1P. Its in-house fan goes on, but the air isn't cooled, and the thing outside makes no noise and the fan doesn't spin. (It worked fine all summer and just broke a couple weeks ago, he happily reports.)

The thermostat is calling for cooling, and the wires from the furnace where they come into the compressor cabinet have 24 volts across them.

Moving along the wires to their destinations, I find the same 24 volts between a black wire at one terminal of the contactor and a black wire at one terminal of a little circuit board next to the contactor. But the contactor hasn't closed the circuit.

The board is 2 inches by 2 inches or less and has 3 terminals, in, out, and ground, or maybe common (I forget). It has a few each of diodes, resistors, transistors and a shiny black almost cube, less than 1x1x1 inch, which I think might be a relay.

What is the purpose of this board, and what is it called??

When I push in the plastic thing in the middle of the contactor, the compressor goes on and sounds fine. That's not proof yet that the problem is the contactor, is it??

I couldn't figure out the diagram inside the cover, or the manual. For example, it didn't have the circuit board afaict. I think I have to make my own diagram, and find out what is the second terminal for the primary of the contactor. Is it the small black wire on the same side, right next to the other black wire that I've already identified??

A new contactor is about 130 dollars. This one is 11 years old but looks like new. I think if it is broken the odds are 50/50 I can repair it. Should I try??

Thanks

Reply to
mm
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Perhaps it's a timer to prevent short-cycling.

Reply to
CJT

Nope. About $20 on grainger.com.

Your description sounds like you have a short-cycle delay timer. You can bypass it to diagnose that component vs the contactor.

Reply to
Richard J Kinch

The board is a delay timer. So that the pressures in the system have time to equalize before the compressor comes back on.

Sounds like you're over your head, here. Might be time to call an AC service guy.

Reply to
Stormin Mormon

Wow. I thought 130 was a lot.

To give myself a pat on the back, I thought of that too, but wasn't at all sure. I'm in pretty good shape now, but I won't work on it again until next Sunday.

Reply to
mm

Well, I was in over my head, but you answered my question for me!

Reply to
mm

However, a couple questions you didn't ask, and I didn't answer.

Reply to
Stormin Mormon

Like "Why is the storming Moron such an idiot?"

Reply to
HeatMan

Stormin Mormon posted for all of us...

Which would NOT be Chris Young alias Stumped Moron

Reply to
Tekkie®

The board you are talking about is a short cycle relay. It keeps the compressor from coming on for a set period of time when some knob is playing with the thermostat. You can replace it, or just take the two wires coming into the system from the air handler and connect them to either side of the contactor in a pinch.

Reply to
Al Moran

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Reply to
Northman

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