Hey all,

I'm hoping to get some pointers. I noticed last week that while the fan on the inside unit was running in my house, the outside Lennox (HL26 I think) was not running at all. I usually don't try to fix this kind of stuff myself, so I called a local HVAC/Electric company to come look at it. They said I needed to replace my t-stat and they wanted me to pay them $300 for the one that they would install. I told them that I would replace it myself. This is something I had done before in another house without issues. I bought a Honeywell t-stat at HD and hooked it up last night. Nothing was different. It still does the same thing it did before. The thermostat is set to cool and the inside fan is running, but the A/C unit outside does not respond. I had read a couple of responses on this site and decided I would take a look at the A/C unit myself. I opened up the side and found the contactor (I think that's what it's called) and I pressed it. The unit started up, so I held it down for a minute or two. Then the condenser stopped making noise and the only thing running was the fan. SO... now that you have the whole story, I guess I have 2 questions.

1.) What could be wrong with the mechanism that tells the A/C unit to start
And
2.) How can I manually override this functionality in the meantime to try to cool my house off. We're baking in here. :p

Thank you in advance for any advice. I sincerely appreciate it. I don't have a whole lot of faith in calling someone new to come look at it after that last technician seems to have advised me incorrectly.

The first thing that you always want to check is to see if there is power to your outside unit. For this you need a voltage meter. One that will read up to at least 300 volts AC. If you fan outside is running that will give you a hint that you are getting some power to the unit but you do not know how much. If you do not have any power to the outside unit you need to find the sorce of your power, A fuse box or a Breaker box or sometimes both. Check the fuses if they are bad replace them... This is not something that you should atempt unless you have some knowledge about elecrticity

What was your problem with your Lennox a/c won't run. My seems to have the same problem. Thanks.

So many things come into play here. For starters did you replace the t-stat with an identical one? There are so many t-stats out there and unless you know what your doing they can look alike but won't operate identically. Ok, you said when you pushed the contactor in the unit started, ran for awhile and stopped. First you need to see why it didn't start via of the controls (t-stat) check and see if you have 24volts coming to the contactor. There are 2- 16 or18 gauge wires going to the coil, check voltage there. If there is no voltage see if your condenser has its own transformer, since the blower is operating its getting a 24 volt signal. If there is no voltage at the contactor the problem is pointing to the t-stat. At the t-stat. jumper the red and yellow wires and see if the unit starts. If it does your stat is either wired wrong or its in-compatable with the unit.

About the stopping after running for 2 minutes, there are many factors here that can come into play. Hi /Lo pressure switches, low charge, the compressors internal protection. Also when you pushed that contactor manually (which is not recomemded) and allowed it to stop for a second and immediately pushed it back in... thats a no! No! You could have caused the problem. A compressor cannot be started and stopped like a fan motor. Pressures are to high for it to re-start.

Hope this helps

Thanks Eschuen for the reply. My problem I believe is either low charge or a bad contactor. Does low charge keep if from coming on? I did push the shrader valve and there is charge. I do have 24 volts coming from the t-stat when commanded. I can push in the contactor manually and it will run continuously. I've only ran it that way for about 3-4 minutes. Worried about low charge and possible damage to the compressor. I'm also thinking it could be the pressure switch because that is the only thing in series with the contactor. Any help would be appreciated. My condenser and furnace filter were clogged previously to the problem. Could that have caused some of the problem. Thanks.