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edteach 07-06-2012 01:17 PM

HVAC question
I have a small one ton lennox system for my home. I had a problem where the contactor would not turn on, so I replaced the contactor and both capacitors. It seemed to work fine for a week but now I have times when the contactor will not turn on and I can go out and bump the side of the unit and it will run for several days. Is there a possible problem from the circuit board? Any help appreciated.

Doc Holliday 07-06-2012 02:20 PM

Did you put in a brand new contactor? Do you have a meter to test for voltage?

edteach 07-06-2012 04:06 PM


Originally Posted by Doc Holliday (Post 959344)
Did you put in a brand new contactor? Do you have a meter to test for voltage?

Yes it was brand new from johnstone, I have a voltage meeter, yes.

Doc Holliday 07-06-2012 05:02 PM

Okay, next time the stat is calling for cool but the outside unit is not running, check to see of the contactor is pulled in. Do this before you shake the thing.

edteach 07-06-2012 05:36 PM


Originally Posted by Doc Holliday (Post 959416)
Okay, next time the stat is calling for cool but the outside unit is not running, check to see of the contactor is pulled in. Do this before you shake the thing.

That is the problem, the contactor is not engaging. I think I have narrowed it down. But my volt meter is broken. The circuit board has two LED lights that blink to show it has power from the Air handler. They were dead and I moved the low voltage wire and it all came alive. So either the air handler is not sending a signal or I have a bad connecting on the circuit board or the board has damage or a crack. I need to test it next time to see where the low voltage is dying. If it comes in from the air handler and the unit or board is dead it must be either a bad connection or a bad board. I am on the way to harbor freight tomorrow to get a digital tester. :thumbsup: Let me know if my logic is flawed. Thanks

Doc Holliday 07-06-2012 05:41 PM

Board on the outside unit? Heat pump or condenser? Either way yes, you are on the right track. I was going to guide you through testing for voltage at the contactor, then trace your way backwards through all components.

When you jiggled the wire the led lit up? And again, is this in the air handler or outside and if outside, heat pump?

Marty S. 07-06-2012 06:20 PM

Pull the board off and look at the back for cracked solder joints.

ben's plumbing 07-06-2012 06:35 PM

agree with all above loose or broken wire...or bad board:yes:

edteach 07-06-2012 06:37 PM

Its a heat pump, it has five wires coming from the air handler. As I moved the wires it kicked on. My tester is dead so I could not test it. I am going to harbor freight in the AM to get a digital tester.
I can remove the board once I get the tester and see where the signal failure is. It works for a time before going out and yes the LEDs were out and came on when I moved the wires. I doubt its the signal form the air handler. I think its either a loose or corroded wire or the board is damaged.

Doc Holliday 07-07-2012 08:59 AM

I'd have to suspect the problem lays with a wire path between the board and the transformer, what gives the board it's power for the led to come on.

edteach 07-12-2012 02:33 PM

It did it again.
Here is what I found, first off I bought a digital multi meter. I am getting the 24 volts from the incoming wire. I then looked at the Circuit board and found that when I moved the board it would make the contactor connect and disconnect just by moving the board when taking it out to look at the back. I did not see and direct cracks in the board itself but I could take my screw driver once I reinstalled it and push the board by the connecting screws for the wire coming in from the air handler and it would make the contactor connect and disconnect. I made sure that the board contacts were not loose and it does not seem to be that, it seems to be the board itself. I think the mounting block is not making contact to the back of the circuit board.

I think that the problem will require a new CB. I am not sure how expensive this is. I don't know if Johnston will have one.

Marty S. 07-12-2012 05:14 PM

Look again at the back side of circuit board and pay attention to the solder joint on the R and C terminals. If it's cracked there will be a baby hair fine line around the solder. Seen many of them crack like that on the C terminal.

hvac5646 07-12-2012 05:53 PM

like the plumber said...maybe loose wire....most common prob on diy contactor replacements...

edteach 07-13-2012 09:35 AM

I don't think its a loose wire. I checked and tightened all the wires. The board must have a small crack in the board because as I said I can take the screw driver and push slightly on the board next to the wire connector block and it will send signal to the contactor, if I let off it disconnects. My problem is Johnston may not carry this CB.

Where can I pick one up if JS does not have one? Lennox? If so where to buy one whole sale?

bobinphx 07-13-2012 11:18 AM

DONT BUY A NEW ONE!!!! (yet)

all you need to do is re-solder the old one. Heat cycles and vibration create issues with circuit boards. By touching up the old solder, the connections will work again!!!!....

if you dont know how to solder, then maybe a new board would be best, but what a better way to learn, I mean its already sort of broken.... how much more broken could you make it!!!!

google how to solder videos, head to radio shack and pick up a cheap soldering iron (25 to 40 watt), get your in touch with your zen soldering skills (LOL) and try it. when done,, celebrate with an adult beverage!!!

just my thoughts...

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