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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I had Honeywell RTH9580 thermostats installed in my Florida

Customer Question

I had Honeywell RTH9580 thermostats installed in my Florida vacation home last fall. This summer, the Lennox air handlers have been sweating in the a/c closet and dripping. A fan blowing on the units is keeping them dry for now. A/C repairman will be meeting me on Monday. I wondered if the thermostats could be wired or programmed incorrectly to cause the condensation issues on both air handlers? They are heat pump systems. It is a new construction home, so I don't have any previous experience in the house with summer temps and the original thermostats.
JA: Did you double-check the thermostat's settings? And what about the filters?
Customer: Yes, we replaced the filters. The thermostat is programmed for heat pump. I got out the thermostat manual and see there are two choices for number of cooling stages: 1 or 2, two choices for changeover valve: cooling or heating, and number of heat pump compressor stages: 1 or 2. If the wrong choice(s) was made, could it cause the condensation build up?
JA: Do you plan on doing the work yourself?
Customer: No. The units are under warranty, so Bayonet is coming out Monday to troubleshoot. I just started thinking about the thermostats and wondered if they could be the cause of the issue.
JA: Anything else we should know to help you best?
Customer: No
Submitted: 2 months ago.
Category: HVAC
Expert:  airheatman replied 2 months ago.

The issue is not going to be with the thermostat settings.Could be that settings in air handler for fan speed need to be changed.If evaporator is running too cold the panels will sweat.Is the ceiling sealed in closet so no attic are can get to unit?

Customer: replied 2 months ago.
Ok. Yes, it's sealed. I've also read that damaged insulation inside the handlers can cause condensation. I think it's odd that both would be damaged though.
Expert:  airheatman replied 2 months ago.

I doubt the insulation is going to be the issue really unless units are over 12 or 15 years.Most likely either fan speed needs to be changed or charge adjusted so evaporators do not run so cold.Do you have a thermometer to check temp of air in and out of air handler?

Customer: replied 2 months ago.
I don't have a thermometer like that. Can I pick one up at Home Depot?
Expert:  airheatman replied 2 months ago.

Yes .WE should have between 17 to 20 degree difference between air in and air out.Any more would indicate coil is running too cold.

Customer: replied 2 months ago.
Ok. I'll see about buying one. What is it called?
Expert:  airheatman replied 2 months ago.

JUst look for probe thermometer hat reads from 1 to 100 degree is fine for this

Customer: replied 2 months ago.
Ok. Thanks!
Expert:  airheatman replied 2 months ago.

Let me know what you find