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Jim952 11-14-2012 04:47 PM

Lennox Outdoor Unit turns on, then off, then on, then off etc.
I have a Lennox m/n 13ACD-048-230-1 outdoor unit. I just noticed that the outdoor unit, turns on, then off after a few seconds, then after a longer time turns on, then off after a few seconds etc. until I went in the house and turned off the thermostat. The thermostat will click on, the indoor air handler turns on, the the outdoor unit turns on and off, on and off, as described above. Took the cover off of the outside unit and depressed the contactor switch, the unit turned on, I let it go after 10 seconds or so and the unit turned off. The capacitor looks OK. That is all I know. Any help for diagnosis and repair would be greatly appreciated.

Marty S. 11-14-2012 06:11 PM

Sounds like the low pressure switch is protecting the AC as it should. Low on refrigerant,plugged metering device or serious lack of air flow will be the potential causes. About all the average home owner can do is make sure the filter is clean and all the registers are open.

Jim952 11-15-2012 07:10 AM

Marty S. Thank you for the diagnosis. Ariflow around outside unit is good, fins and all are clear also. As for the metering device, what is that? How could I check and replace? Low on refrigerant, that would mean a leak? Or is it possible that refrigerant needs to be replenished periodically, although I don't think so. Unit has been running trouble free since 2007. Please let me know if you can. Also, what is are cost for refrigerant leak check and fill? Thanks again.

Jim952 11-15-2012 09:20 AM

additional info.
Started the system today to time the cycle of running and shutting of and the outside unit did not turn on at all. I don't know if this information helps diagnose at all.
Thanks again for any and all help.

Doc Holliday 11-15-2012 09:26 AM

if by pushing in the contactor the condenser stays running then you're going to need a tech to come out if indeed it is low on refrigerant and the pressure switch is shutting it down.

Jim952 11-15-2012 09:33 AM

Thank you for you reply. So if I set thermostat to low inside the house, inside air handler turns on, I then go out and depress the contactor switch manually and hold it, the outside unit will shut down on it's own even though I am holding the contactor switch? This will mean that I am low on refrigerant.

Doc Holliday 11-15-2012 10:06 AM

If the low pressure switch is on the low voltage side than it should stay running if the contactor is pushed in.. And you don't need to have the stat on to push in the contactor.

Jim952 11-15-2012 11:05 AM

Doc, I pushed in the contactor and the unit ran, held it for 30 sec or so. So this most likely means low refrigerant? Which means a leak?

Doc Holliday 11-15-2012 11:10 AM

It's a good indication that it's low IF you have a low pressure switch in that condenser. Look on the inside of the unit through the top. On the bigger copper refrigerant line you should have something that looks like this, with two wires attached to it. You may also have one on the little line but that would be a high pressure switch.

Doc Holliday 11-15-2012 11:14 AM

What those switches do is protect the compressor from blowing up. Refrigerant has oil in it to keep the moving parts lubed and to keep the compressor cool. When you have a leak that switch will trip out at a certain level so the compressor doesn't run hot and burn up.

Let's you know you have an issue that needs addressing.

Jim952 11-15-2012 11:25 AM

Thanks Doc, I do see that the large copper pipe inside the unit has a switch with two wires coming out and going up. So most likely this is "tripped" by low pressure in the line and will not allow the contactor to turn on or stay on?

Jim952 11-15-2012 11:38 AM

Would you let me know what a competent A/C repair guy would do. Empty lines, fill with nitrogen, and or dye, check for leaks? Is there a real way to plug leaks with an additive? I was trying to avoid $100s in repair especially before Christmas holiday but I if I'm spending $ I would like it done correctly.

Marty S. 11-15-2012 04:24 PM

Jim a contractor is going to get the unit to run then check superheat and subcool to find out if it's a lack of refrigerant or a restriction in the refrigerant flow. If it is low then yes it has a leak. Most leaks can be found with an electronic detector quickly. The location of the leak will determine repair costs. It could be a $2 part or a $1000 part, no way to tell from here. Avoid the leak seal stuff.

Doc Holliday 11-15-2012 05:05 PM

He can just add refrigerant if you don't want to pay for the repair. Mind you now, that refrigerant may last a full year or it may just last a full day. No way to know until it's gone again.

You can get away for maybe $300 this way, maybe a bit more, maybe a bit less. Service call out to the residence plus who knows how much refrigerant and what the company charges for said refrigerant. Could be $50-$100 per pound.

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