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SOLVED. AC Thermostat help
Posted on 7/21/23 at 7:44 am
Posted on 7/21/23 at 7:44 am
Solution: In line drain float switch is tripping due to slow draining. That’s why it comes on every now and then.
My in laws have a nest thermostat and suddenly the thermostat will just turn off along with the AC unit. If we turn off the breaker for a couple minutes it will come back on for half hour or less.
I checked the pan to see if it could be the float switch but the pan is dry. I don’t know much about AC wiring but I’m pretty handy with a voltmeter. Any help greatly appreciated.
My in laws have a nest thermostat and suddenly the thermostat will just turn off along with the AC unit. If we turn off the breaker for a couple minutes it will come back on for half hour or less.
I checked the pan to see if it could be the float switch but the pan is dry. I don’t know much about AC wiring but I’m pretty handy with a voltmeter. Any help greatly appreciated.
This post was edited on 7/21/23 at 9:13 am
3
Posted on 7/21/23 at 7:52 am to skidry
You say that the thermostat is off. Does it still have power? And does the air handler still have power?
There should be some lights on the control board that are still on.
Next time the thermostat and Air handler turn off, check to see if you have 24 VAC at the thermostat. Make sure you are on the VAC setting (not VDC).
The air handler supplies VAC to the thermostat. If you don't have VAC at the thermostat, then something is going on with the air handler controls. It could the control board or the power supply.
And you say that you turn off the breaker for the air handler. Is that breaker still in the on position or has it tripped?
There should be some lights on the control board that are still on.
Next time the thermostat and Air handler turn off, check to see if you have 24 VAC at the thermostat. Make sure you are on the VAC setting (not VDC).
The air handler supplies VAC to the thermostat. If you don't have VAC at the thermostat, then something is going on with the air handler controls. It could the control board or the power supply.
And you say that you turn off the breaker for the air handler. Is that breaker still in the on position or has it tripped?
This post was edited on 7/21/23 at 8:01 am
Posted on 7/21/23 at 8:08 am to tdme
When it happens the thermostat is totally dead (no display at all) and the unit will shut off completely.
The breaker is not tripped. We have to turn it off and then back on again. This may be unrelated and coincidence as we have not tried just let it sit for a few minutes to see if it will come back on again.
Do you know the colors of wires I need to check the voltage across?
Oh and thank you for your quick response.
The breaker is not tripped. We have to turn it off and then back on again. This may be unrelated and coincidence as we have not tried just let it sit for a few minutes to see if it will come back on again.
Do you know the colors of wires I need to check the voltage across?
Oh and thank you for your quick response.
This post was edited on 7/21/23 at 8:09 am
Posted on 7/21/23 at 8:39 am to skidry
If the thermostat goes dark, then I think that would shut off the air handler.
You need to know if the thermostat still has VAC.
It has t0 be either the thermostat itself or the air handler's control board or power supply.
You need to know if the thermostat still has VAC.
It has t0 be either the thermostat itself or the air handler's control board or power supply.
This post was edited on 7/21/23 at 8:44 am
Posted on 7/21/23 at 8:47 am to skidry
It sounds like you're talking about scheduling here. Mine used to do that as well until I looked at the schedule and reset it.
Say you set the thermostat to 73 yet it's a cold day outside so you bump it up to 78.
Well it's a "learning thermostat" so next week, the same thing will happen. So it's still on, just not blowing air b/c the temp is set higher.
Say you set the thermostat to 73 yet it's a cold day outside so you bump it up to 78.
Well it's a "learning thermostat" so next week, the same thing will happen. So it's still on, just not blowing air b/c the temp is set higher.
Posted on 7/21/23 at 8:59 am to skidry
In HVAC professional forums I follow, HVAC techs do not recommend use of Nest thermostats because of potential problems and damage they can cause to HVAC equipment. I’ll link a few threads with responses by HVAC techs to Nest thermostats posed by a homeowner.
LINK
LINK
LINK
Not saying the issue is with the thermostat, could be a furance/air handler control board or wiring, but…..
This might help as well How to Test a Thermostat with a Multimeter - this HVAC tech has an excellent Y/T channel for diagnosing HVAC issues.
LINK
LINK
LINK
Not saying the issue is with the thermostat, could be a furance/air handler control board or wiring, but…..
This might help as well How to Test a Thermostat with a Multimeter - this HVAC tech has an excellent Y/T channel for diagnosing HVAC issues.
Posted on 7/21/23 at 9:11 am to CrawDude
It ended up being the in-line float switch. I didn’t realize there were 2. The pan is fine but the drain coming directly out of the air handler also has a switch and that drain is clogged. The switch must be just low enough that the switch is tripping before it over flows into the pan.
The Nest has a rechargeable battery but the unit was cutting out so much that the battery eventually went dead.
Thanks very much for all the help.
The Nest has a rechargeable battery but the unit was cutting out so much that the battery eventually went dead.
Thanks very much for all the help.
This post was edited on 7/21/23 at 9:33 am
Posted on 7/21/23 at 9:48 am to skidry
quote:
It ended up being the in-line float switch. I didn’t realize there were 2. The pan is fine but the drain coming directly out of the air handler also has a switch and that drain is clogged. The switch must be just low enough that the switch is tripping before it over flows into the pan.
Thanks for the update - same thing happened to me a few years ago, thought I had a thermostat issue but it was a clogged drain line with the safety switch cutting power the control board, thermostat.
Posted on 7/21/23 at 10:42 am to skidry
quote:
in-line float switch
I installed one of these when my pan overflowed (pan switch was dead). I also pour a teaspoon of spa chlorine granules into the float switch trap (with a water chaser) every so often to keep the drain line clear. No problems in 15 years.
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