- AC intermittently not working

[rpforumuser]

Hello, I have a Luxaire A/C system with an outside condenser and an air handler in my attic (model # faaf-f036ra). I have owned the house for 3 summers now and it's always worked perfectly. Early this year when we had the heat wave, I turned it on to make sure everything was working, and to my surprise, nothing happened. The fan wouldn't even turn on from the "on/auto" switch.

My initial concern was that a wire was disconnected or something (I had insulation blown in the previous fall, and there was power at the condenser and the thermostat). A few weekends later when it was cool I got ready to go up in the attic and dig around the air handler to check the wires from the tstat (it's all buried under insulation now). I quick switched the fan on before heading up and to my surprise, it started up. When I switched to cool mode, everything ran as it should.

I checked it a few more times over the last few weeks and it always came on. Imagine my surprise this last weekend when I turned it on to actually use it, and it was dead again (no fan, condenser, anything). No noises like anything was trying to start. Just - dead. I left the fan switch "on" and the tstat set to cool. About two hours later it started up and ran all weekend just fine.

My thought is this has something to do with heat. Both times it's been "dead" were hot, sunny days with outdoor temps near or at 90 deg. F. I imagine the attic is way hotter than that. I wondered about a high-temperature switch that would shut it down, or maybe the condensate pan overflow switch. What gets me is that it seems like the internal temps of the unit should be cooler since it's covered with insulation now. It seems like some sort of a switch because it's not like the condenser is starting up either. Another idea is the thermostat... which I could change out to rule out if/when this happens again.

Any thoughts would be greatly appreciated! Thanks in advance!

[rpforumuser]

Thanks - I'll replace the batteries and see if that helps. Just bizarre to me and I wondered if there could be something else going on that will need servicing. Unfortunately it's hard to schedule someone to come out when it's so unpredictable!

[Freon]

It is possible there's a cold solder joint on the control board at the air handler. Go to the air handler and label the thermostat wires with tape and the corresponding terminal they connect to at the control board. TURN OFF the power to the air handler. Disconnect all the thermostat wires. Now CAREFULLY use a jumper wire firmly attached to the R terminal. That's 24 volts, AC. Now make sure the unattached end of the wire is not near any metal object. Maybe get someone to help... turn on the power now. CAREFULLY touch the bare end of the jumper wire to the G terminal. The blower motor in the air handler should start. If the blower does run when you jumper it, try touching the end of the jumper to the Y terminal. The outdoor condenser should start. If both run then check the thermostat and its wiring.

If neither the fan nor the condenser run, then I suspect the control board. Check with a multimeter that there is 24 volts AC between the R terminal and the common, usually C, on the control board. If you have 24 volts AC and can remove the control board, inspect each solder joint and component for signs of problems. Turn off the power and reconnect the thermostat wires.

Be very careful with the power on when doing any work at the control board. You don't want to inadvertently fry the control board.