DIY Home Improvement Forum banner

Lennox 12ACB48 - Help

5408 Views 57 Replies 9 Participants Last post by  wreedlbz

I recently purchased a home with a Lennox 12ACB48 unit. The unit would not cool very well so the sellers had it serviced and freon was added and fan motor replaced I believe. Vent temps went from mid 70s to 59-64 around the house. Today it was very hot outside (Houston TX) and the unit stopped cooling. It was blowing 84 out of most vents and the compressor was blowing somewhat cool air out the top. I turned the thermostat off and back on after a few minutes and everything seems to be fine for now.

Can anyone help me with what is going on? My uncle a competent engineer came over and put gauges on the system and they were OK he said. I have a service call scheldued with my home warranty, but I trust this site way more than any tech from the home warranty company.

Any ideas as to what is going on?
1 - 13 of 58 Posts
do you have a meter with a continuity (ohms) function? I'm willing to bet that the compressor has open windings meaning it's shot.
Yes I believe I do.

Well it might only have the thermal overload switch open in it if it got too hot. Without doing anything to any wires run your water hose on the condenser, mainly on the compressor for a good ten to fifteen minutes.

If it was running and got too hot then running water over the compressor will cool it off enough to close that switch which is internal versus being a reset button someone can simply push.

if you don't run water over it you're looking at a possible 4-6 hours for it to cool off on it's own.

again, this is only one possibility, that the thermal overload is open.

try that and if it doesn't come on than I'll walk you through how to test the motor with continuity.
So now we know that your comrpessor is getting too hot which means the refrigerant levels need to be checked and the condenser coil needs to positively be cleaned. That and the evaporator.

I'm not suggesting that the windings aren't weak and the compressor is not on it's last legs as that very well could be the case (although the thermal overload switch is there to protect the compressor) but these are the reasons compressors go out; lack of air flow (restriction/dirt) through the inside (evaporator) and outside (condenser) coils and or refrigerant problems which stem from lack of air flow or leaks.

I'd sure like to know the pressures on that thing once it's running for about twenty minutes. I don't take it you have a set of refrigerant gauges, do you?
OKey dokey, water did it. It is cooling again. This is now the third time this has happened. So far we have cleaned the coil, charged the system and put a 5 2 1 hard start kit on it. What else should we do?

You cleaned the outside condensing coil?
My uncle has gauges and he is in San Antionio. So I just left for 30 mins and came home, compressor outside was COMPLETELY OFF, air handler in the house was stilling blowing. I dont know what to do now.

run some water over the compressor again until it comes back on and then rinse the condenser from top to bottom on all sides and once finished do it again and again and then again. use some pressure on the water, like your thumb over the end of the hose type pressure, to remove any possible dirt from the coil (you're not rinsing the outter casing, you're trying to get the inside so spray in between the panel holes/slits from top to bottom), all while the system is running. water absorbs/removes heat better than air so while the system is running you're helping the hot vapor in the condensing coil condense into a liquid as it dissipates the heat it extracted from your living space inside. again, if your CONDENSER coil is dirty then it can't let that heat go and it's adding to the heat from the compressor simply running.

continue to run water over the condenser coils and see if after your home reaches desired set point and the system cycles completely off, both inside and outside, if it comes back on.

without gauges we can't tell exactly what is causing the compressor to overheat. if a condenser coil is dirty than the head or high pressure will be abnormally high not too mention once again it will overheat.
See less See more
You should not spray it down with the unit running this would cause you to push anything that is in the fins of the coil to be compacted even more into the coil. The proper way to do this is to remove the top of the unit with the power OFF! And then spray the coil from the inside out. Some hardware stores also carry mild coil cleaner that will aide you in the process of cleaning the coil. After the coil is clean, if need be you can run water through it from the outside, in. The thing to remember is that during normal operation the cond. fan motor pulls air through the outside of the coil and exhausts the air out the top so by this process everything is getting stuck and pulled into the coil from the outside in. You want to spray from the inside out as to not compact the debris further into the coil.

on a true condenser coil cleaning this would be true but the suction pressure of that fan is not stronger than basic thumb pressure from a water hose and it will work, especially on grass and even loose dirt. Besides, this is just for a diganosis but even when the system is running it easily works. I've done it hundreds of times and I'll do it thousands more.

have you not seen the pictures of my cleanings? You're talking to the number one condenser coil cleaning expert in all of Texas. :laughing:
How do I check that?

you can visually look at the thing and see if it's stuck closed. I think that this is what JJboy is getting at and it could very well be the case. The system will satisfy on the inside (reach desired set point on thermostat) and cut the call for cool off but if the high voltage contactor on the condensing unit is stuck closed then it keeps on running and overheats.

I have pics, give me a second.
From a few weeks ago, contactor that was stuck closed and causing the compressor to overheat from a few weeks ago.

See less See more
I did check the contactor, I had 243V on each side.
You had 243 across two legs at the contactor of 120 which in all actuality were 12? per leg or each side. If you check from one terminal to ground (you can use the ground lug in the condenser) it will show you 12?. From terminal to terminal is 243 which is the total of two individual legs, single phase.

I have a strong hunch that you're going to need a new compressor.
Then that's it, bud. Congratulations!

I was going to also suggest that possibly the breaker was weak..good job!
Does this make sense? If the fan motor was cutting out if would over heat the compressor causing it to shutdown?

I think I had 2 problems. 1 was the cap on the compressor and 2 was the cap on the fan motor. I just didnt find the fan motor cap the first time because it was disguised.

Make sense?

It makes sense that if one goes out the other does not work so yes. A condenser contains extremely hot refrigerant in vapor form, from cool low pressure vapor to hot high pressure vapor right through the compressor. The fan draws air through the coils, cooling the hot vapor off enough to condense into a liquid to be shot back up to the evaporator coil to then evaporate and that is the complete cycle so guess what happens when the fan goes out in the condenser? Yup, that vapor isn't cooling off. Combine that with the regular heat of the compressor running and too hot and overheating is inevitable.

You should be good, but I'd really like to know the pressures. Did you get the gauges?
1 - 13 of 58 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.