As title states, on occasion the attic air handler will run and blow room temp air and the outside 2.5 ton Lennox compressor will not run. The thermostat reads “cool on” like it should. Since the compressor is not running, the indoor temp does not satisfy the thermostat setting and the air handler just keeps blowing room temp air. When this happens if I turn the thermostat to “off” let the air handler shut off (about 2 mins) then turn the thermostat back on again everything is working as it should for what could be a few days to a week, then it may occur again. Quick google searches point towards a contactor issue and less likely a capacitor issue. I am going to go through the thermostat settings to see if they are the same as my downstairs thermostat, maybe a compressor protection setting is causing. Has anyone had a similar issue that would like to share your knowledge? I like to DIY the most I can before calling in the pros. Thanks for taking the time to read!
Air handler running, compressor not (until thermostat reset)
- Thread starter flan
- Start date
slow
Well-known member
I would check to see if the outside contactor coil is being powered, that would separate if it is a low voltage control issue (my guess) or an issue on the high voltage side of the system (contactor, fan, compressor over heat ...) Some units also have delay timers to keep from a quick restart. How long do you leave it running in "cool" when the compressor is not running, like 2 minutes or 25?
Could be any number of things. Electronic thermostat? That'd be the first place I'd look. Programming could be off - I've seen more stats than I can count that the day/time was all wrong (or factory program still active) and customer paid a service call for me to enter the program they wanted. They want cool on Tuesday but stat thinks it's Sunday - that kind of thing.
Electronic board in condensing unit? Time delay function in it could be sticking - never lets comp come on but recycling it frees it up. Contactors and capacitors are pretty maintenance free, though caps of late have been getting real cheap. But if one of them goes bad recycling rarely would bring it back on. Check contactor contacts for insect infiltration. If an ant of spider is walking thru the contacts when it calls for cooling the contacts close and burn the bug guts with high voltage. That can hang up a contactor or casue intermittent working.
Loose/corroded connection somewhere. Stat sub-base, bad stat wire, wire nut connection, control board attachment, or component hook up. Any of these gets corroded or loose - intermittent ops.
Electronic board in condensing unit? Time delay function in it could be sticking - never lets comp come on but recycling it frees it up. Contactors and capacitors are pretty maintenance free, though caps of late have been getting real cheap. But if one of them goes bad recycling rarely would bring it back on. Check contactor contacts for insect infiltration. If an ant of spider is walking thru the contacts when it calls for cooling the contacts close and burn the bug guts with high voltage. That can hang up a contactor or casue intermittent working.
Loose/corroded connection somewhere. Stat sub-base, bad stat wire, wire nut connection, control board attachment, or component hook up. Any of these gets corroded or loose - intermittent ops.
Terry D
Well-known member
Is the condenser fan running when the compressor is not
Really it runs until either my wife or myself notices the upstairs is warmer by several degrees than the downstairs. So potentially up to an hour or more.
It is a Honeywell electric thermostat that we will either leave on permanent hold or in the off position. The circuit board was new at the beginning of last year as it was not allowing the unit to go into 2nd stage cooling. I did check out the wiring and found the thermostat wire entering the unit had either the insulation chewed or rubbed off through vibration on the unit. There was copper visible, not a lot but I suppose it could of grounded out on the metal opening it passed through. I stripped back and **** connected the 3 wires then re secured to prevent future issues with that. The contactor and capacitor appear original to the unit, 2010.
No, the fan is not. When it happened yesterday I went outside just to confirm the compressor wasn’t operational. I felt the line set and they were ambient temperature. The 1st floor unit was humming along side of it so I couldn’t detect any strange noises. I suppose if it rears it’s head again one of my first steps will be to check for 24vac at the contactor? Also make sure 1st floor is off so I can listen for either the fan or compressor trying to start up.
Terry D
Well-known member
When it does it again, check for 24 volts at the contactor. Also check for 240 volts on the line side of the contactor. Sounds like you may have a faulty thermostat. If you jump R, G and Y together at the stat, your blower and condenser should come on
I caught it in the act just a little while ago. No 24v at contactor. I did have 240 at the contactor. The unit has a control board and I noticed a solid red led and the green was flashing 6 times. The chart inside the door says that’s a “low discharge line temperature” fault code. Turned off thermostat and turned it back on and the unit is cooling again.
Some sensor is catching something out of spec. Like the "Check engine light" in a car. Aims you in the right direction, gotta figure out the exact cause yourself.
While you're in there examine closely the circuit board itself - check every component where it's soldered to the board. Any burns of discoloration (usually the resistors) indicate heat is getting to it and might lead to an issue.
While you're in there examine closely the circuit board itself - check every component where it's soldered to the board. Any burns of discoloration (usually the resistors) indicate heat is getting to it and might lead to an issue.
Disconnect the condensing unit from 240VAC. Apply compressed air to the control board until clean. Find input from the temp sensor and work it on and off the connector a couple of times. Push the reset on the low pressure switch for good luck. If it once worked, it might work again. Turn power back on to the unit, call for cooling and observe. Where did the black goo come from? This is a solution for the northeast; if you're in AZ all bets are off.
The “black goo” is old mouse pee/poop. Apparently at one time there was a mouse living on the shelf in there. I gave the wiring a once over for chew marks and only found evidence in the thermostat wire I mentioned earlier. I’ll look for the low pressure switch, and follow the wire up to the control board as you suggested. The board was replaced at the beginning of last year so maybe the spade connector is loose on the board.
I don’t want to claim victory quite yet, but the last 2 days it has been running as it should. I unplugged the low discharge line temp sensor from the circuit board. This sensor is supposedly only for heat pump operation so I don’t know the relationship to the cooling side of the unit. Will continue to monitor and give an update in a week or so..
