Honeywell Wifi Thermostat wrong voltage?


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Old 07-01-17, 04:05 PM
J
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Honeywell Wifi Thermostat wrong voltage?

Earlier this spring I bought a new Honeywell wifi thermostat to replace the 5-2 Honeywell thermostat we had for 12 years that quit on us.

It seemed to function fine for the first couple of months of a very cool spring (Northern VA) with a day of heat and another day of cold, etc. Now that the heat has arrived for good I think something is wrong and the previous couple of months the system appeared ok because the house is well insulated and the temps were staying away from extremes.

A couple of days ago I noticed that it was REALLY getting cold in certain portions of the house that don't have a lot of circulation. I also noticed the AC was running a LOT, like hours on end. i started taking a look at stuff and noticed that the thermostat was showing 77 degrees indoors even though I had it set for 74 on a program most of the day except the middle when we are out and it goes to a 76 setting. I put a digital air thermometer next to the thermostat and it showed 74.3. I put an infrared thermometer on the metal floor registers and they show low 60's.

After some reading on the net I discovered some feel they have calibration issues and they need to change the offset. I changed it to 3 degrees (wasn't pleased, I feel the thermostat should be more accurate than that) and it seemed to be in line with the other thermometer for the last couple of days. However, the system is still running almost constantly and still running even when the thermostat shows the room as the set temperature. Here is a pic of this situation:

I called Honeywell today and told them all above. The person on the phone said they stand behind the thermostat calibration and it might be a voltage problem. While on the phone I got out a meter and they had me pull the front off the thermostat and check the voltage between the R and G pins. I checked by touching the solder points on the outside of the wires so I didnt' have to pull them out. I got 3.0v. They said that was the problem and that the thermostat requires 24v and the thermostat is probably reading incorrectly because of that. I read up on the 24v issue and I see it does need 24 and I only have 3. That said, I think my system is new enough tech (2005) to be supplying the 24v. So have I wired something wrong? Even if the voltage caused the incorrect temp reading, would that cause it to continue to run after the temp has been achieved?

Thanks again for any help.


Some general info and photos of my wiring:

Register temps: low 60's
Thermostat setting: 74
Honeywell wifi thermostat
Goodman gas furnace with AC installed in 2005 with house construction
New control board in 2016
Aprilair whole house humidifier with bypass










 

Last edited by jeeden; 07-01-17 at 04:21 PM.
  #2  
Old 07-02-17, 12:17 PM
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It sounds like you need a new voltage meter. Nothing would run if you had 3 volts.
Did you use the VAC setting on your meter?

The thermostat displays whole numbers but it actually controls the system using one digit below the decimal point. If it is set at 74 and reading 74.5 it would display 74 but continue to run the system.

Adjusting the calibration is not an option with their lower end units so it is good that you chose a higher end unit. I would seal the hole behind the thermostat that the stat wire runs through to allow a more accurate reading.
 
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Old 07-24-17, 04:13 PM
J
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Just to follow up. You are correct that the temp is sitting int he 74.x range so it is technically not making it to 74.0 until after some time and it shuts off.

Voltage meter is good, problem was measuring the voltage on the board instead of the wires. Appears to be working fine, I think the system is just getting old and maybe the thermostat is a little more sensitive than others I've had.
 
 

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