Ac voodoo


Old 08-01-20, 01:09 PM
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Ac voodoo

My ac is acting up. I have a Lennox unit, only a few years old. Started off a few weeks ago it wasnít coming on and the unit outside was loudy clicking and buzzing. So after some research I replaced the contactor and capacitor. Boom it was working again no issues. A month later. After a few weeks of summer heat and ac working hard to keep us cool. Ac stops working. Starts clicking and buzzing. After research. I started checking the contactor with a multimeter. Got 18 ohms. Checked the old contactor. Got 18 ohms. The new contactor has some signs of discoloration from the arcing around the plunger so I took it out and put the old contactor back in. Now itís stopped buzzing. But there is a faint clicking. So I checked for 24v with the multimeter. I checked contactor and the spliced wires from the house and got nothing. Wasnít getting the 24v from the thermostat. So not here comes the voodoo. So I go inside and start checking the voltage in the thermostat and itís there. I put the faceplate back on the thermostat and said f#%* it. Iíll call in a professional. I decided to go back out to the unit and check for 24v. And wow. Now thereís voltage. 26 volt. I plugged in the power disconnect and the ac kicks on and is running with no problems.
So the thermostat has never been off since It was installed with the new Lennox unit. I donít understand why I donít have 24 volts at the contactor and than it suddenly comes back. Thereís no breaks in the wire that I can see. No blown fuses. Not tripped breakers. Contactor. New and old both work. Does anyone have a idea?
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Old 08-01-20, 01:32 PM
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Welcome to the forums.

There are protection sensors inside the condenser. There is usually a low pressure switch and sometimes a high pressure one. If you are low on refrigerant.... the low pressure switch opens to keep 24v from the contactor.

If you have a problem again..... locate the splices where the thermostat wire comes into the unit from the house. Check for 24v directly at the splice. If it's there but not at the contactor.... you need a recharge.
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