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-   -   Home AC not cooling - help! (http://www.houserepairtalk.com/f8/home-ac-not-cooling-help-4424/)

TexasKid 06-14-2008 11:39 AM

Home AC not cooling - help!
 
Howdy folks - I've been lurking for awhile but just joined. I can make most repairs and figure a lot of stuff out, but I'm stuck on this one. Any help, advice, or suggestions would be appreciated.

I have a Carrier furnace in the attic - attached is an AC evaporator and a fan I think. The condenser unit outside is a Lennox. Symptoms: condenser fan is turning but not discharging warm air out of the top of the unit, freon line in the attic is hot (not sweating), condensation pan is dry. I took the condenser apart as well as I could and didn't see any "burned" wires anywhere. I couldn't reach the compressor to see if it was hot - but system has been off for a day anyway - I figured out Friday afternoon it was not cooling and turned it off. I've turned it back on but still not cooling. Before I call a pro, I have two guesses: Compresser bad and needs to be replaced or, the evaporator coil has a leak and all the freon is gone. Any suggestions, ideas as to what I might look at, advice? I'd like to avoid spending a lot of money - I'm already so broke I can't pay attention. Thank you - this is a great forum!

glennjanie 06-14-2008 09:09 PM

Welcome TexasKid:
Open the electrical panel on the condenser unit and find the contactor (it is a magnetic switch), use your screwdriver to push the center of the contactor in and see if you can hear the compressor running. That will eliminate the question of high voltage power and the compressor's ability to run.
If the compressor will run, you probably have a low-voltage problem, which your thermostat works on. Check the small wires with a voltmeter for 24 volts. Trace it back to the transformer, see if there is 110-120 volts there on one side and 24 volts on the other side.
I would not suggest a bad compressor or lack of refrigerant to a service man. Those are the two most expensive things he could repair. Your refrigerant is not used up and does not wear out, it can only leak out. Find the copper refrigerant lines in the inspection panel, take the little cap off either one and use your screwdriver to depress the valve (looks just like a tire valve) and see if there is pressure there.
For the compressor, you will need to remove a larger side panel, turn off the power, remove the little spring clip and plastic cap over the terminals. Using an ohmmeter, check the ohm reading from each of the 3 terminals to ground, write down the reading on each terminal. The readings on 2 terminals should equal the reading on the third terminal.
Let us know how these tests turn out and we can go further.
Glenn

TexasKid 06-15-2008 10:01 AM

Glenn,

Thanks for the advice. I'll go out there and look at it again. A couple of things crossing my mind when I read your reply are: Not sure what the contactor looks like. Assuming I can find it, will I be able to hear the compressor over the fan noise? Speaking of contactors, I saw something yesterday that looked interesting inside the condensing unit electrical panel - initially, I was looking for burned wires. Didn't see any burned wires but I did find this object - hard plastic, red, about as big around as a quarter and mounted inside the unit wall. It had a rubber (I think) red button on it. I was wondering what the heck it was for, but then I noticed that it was disconnected, as if bypassed at some point in the past. There were two blue wires leaving it, one had been cut and the other looked like it might have been in a wire nut, but I could tell the end was not fresh and it just looked old like it had not been connected to anything lately. There were two wire nuts in the immediate vecinity joining the low voltage to other wires, and heading up through a hole to another part of the electrical panel in the unit. I don't know how old this Lennox condenser is, but it could be as old as '89. Next time I'm looking at it, I'm going to take some pics.

The transformer for the low voltage - where might I find this? Would it be in the attic mounted on the furnace unit? I remember seeing the same wires up there, just can't remember what they attached to.

And, finally, I'll check that compressor. Getting to it is a problem. There isn't anything "user friendly" about where the unit is sitting. I can open it up well enough to peek inside, but may have to move it to really get it open. Can I take the top off and remove the fan blade? I'm afraid if I move it, I'll mess up the copper lines. Well, I'm a big boy... I think I can handle it. I guess none of this stuff is too easy. I killed two wasps nests yesterday just getting into the unit...

I'll let you know how it turns out. Thanks again!

JC

glennjanie 06-15-2008 01:05 PM

Hello JC:
Yes, the transformer may be with the furnace. About all you can do is trace the wires until you find the transformer.
The contactor will be a 2 to 3 inch square device with flat copper pieces running paralell across it. The power line will be attached to one side of it while the othre side wires go directly to the compressor and fan. It will also have 2 small wires attached which activate the magnetic coil to pull the contacts in.
You will be able to hear the compressor unless it is a Copeland Scroll, which will be a tall, 5 or 6 inch round compressor. While most compressors have an oval shape from the top. The wires connected to the compressor are the ones that most often burn into. I was happy to see that you looked for burned wires first, that is the problem in 8 out of 10 cases.
Yes, the top is sometimes the best way to get access to the compressor. I would not recommend moving the condensing unit because it will either break or kink the copper lines.
I will be watching for the results and I hope it works out soon for you. Glenn

handyguys 06-16-2008 11:18 AM

As glenn said, refrigerant is not used up. Leaks do to develop over time. Replacing refrigerant is not expensive, its the time to find and repair a leak that costs. My guess, once electrical has been eliminated, is that you have no refrigerant.

kok328 06-16-2008 05:20 PM

That button that you found w/the wires disconnected is the high pressure cut off switch. It is design to shut down the compressor before it destroys itself internally.
I hate to be the bearer of bad news but, it sounds like the compressor is shot.
Do you have a variable speed fan relay and/or crankcase heaters installed?
Also, there is very little play in the copper lines w/o risking creating a leak.

TexasKid 06-18-2008 06:46 AM

kok328,

Does it make sense that that high pressure switch could have been disconnected or bypassed? I can tell that those blue wires have not been disconnected to anything recently. Seems odd to me - why would someone do that?

I don't know what a variable speed fan relay or a crankcase heater would look like or where they'd be. If I were looking under the hood of a car, I could tell you anything, but when it comes to identifying HVAC stuff, I'm a little ignorant.

Thanks though - you're making me think!

kok328 06-18-2008 09:21 AM

If the pressure switch went bad, you have to evacute the system, replace the switch and recharge it (something that not everyone has the ability to do). So to bypass the switch, is a quick fix. To not replace it is risky.
The variable speed fan controller would be located on one of the 4 corners of the condensing unit. This varies the speed of the condensor fan so as to not cool off the freon too much during cold weather. If this controller goes bad, you may not be cooling the freon enough or too much. Either case would be a short life for your compressor. The crankcase heater or heat band would be located around the bottom of the compressor itself. The heat band's job is to keep the oil in the compressor at a certain viscosity during cold weather usage.
Your really going to need to put some guages on this system to determine the state/health of your compressor. You could also have a clogged dryer/filter which also requires the system to be evacuted and recharged after replacement.

TexasKid 06-19-2008 09:30 PM

The verdict is in. The compressor is locked up. My AC guy - a guy I think I can trust but don't know that well, came out and looked at it for about 20 minutes and decided that was it. The condenser is a 1988 model, and he says replacing the compressor would/could be almost as expensive as replacing the whole thing. IS THIS TRUE? But I understand the probable delimma of puting a new compressor in a 20 year old unit. I saw a new 4-ton Carrier compressor on the internet for $500.

He says he can get me a couple of different 4-ton condenser uints for $2,000 to $2,400. I've seen a couple of new 4-ton units on the internet for about $1,200. I also saw some used and not too old 4-ton condenser units on the internet for around $500 and installation for another $500. I don't want to spend $2,000 or more if I can spend half that. What do you guys think? The AC guy I know - is he taking advantage of me a little bit? He's probably going to make a lot more money if I buy one from him. If I don't, he'll probably charge me more to install. WHAT DO YA'LL THINK? I just want to be dealt with fairly.

glennjanie 06-20-2008 10:30 PM

Hello JC:
My experience with Air Conditioning Technicians is that they frequently have to take bankruptcy and seek other employment; quite the opposite of a person who charges too much.
Your unit is way over its design life of 12 years; I would replace the whole unit. The $500 unit would be a good buy if it is less than 5 years old and your friend would probably be willing to work with you at the $500 labor price. However, he will not want to be responsible for the warranty on the unit or pay for any extra parts or new refrigerant, that's only fair. I can understand not wanting to go for the $2,000 or more; when you can get going again for $1,000 to $1200. The used unit may last for only 10 more years or could go for another 20 years. There's no sure way to predict the outcome but you may be in better shape to go for a whole new outfit after 10 years.
Glenn


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