09-22-202310:35 PM - last edited on 09-26-202302:21 PM by EdmondB
Hello, I'm having problems with my Heat Pump and Google Nest.
What I have: I own a Nest Learning Thermostat 3rd Gen. I purchased this back in 2020 It is attached to a single Payne Heat Pump system. My Nest has successfully changed between heating and cooling and matched requested temperatures for the past 2 1/2 years. In short it has worked well.
The Problem: Recently when I switched the system from cooling to heat it started producing a repeating ticking noise. It could be heard in the air handler and also outside where the condenser is. The Nest reports no errors of any kind functions as normal.
My Finding: After ruling out wire degradation, fuses and a whole lot of voltage measurements and troubleshooting I have narrowed the problem down to 1 wire, the ( OB ) the Heat pump Orange wire.
As I understand it, in normal operation the Nest is switching from Heat to Cooling by applying constant +24 V AC to the condenser reversing valve. This essentially switches the value from heating to cooling. This is supposed to be a constant +24V supply.
What I have found from doing my measurements during this conversion process is the Nest starts by sending around 26 or so volts but then immediately drops down to around 22 V then rises back up again to 26V this constant voltage oscillation drives the reversing valve on and off since it is designed to engage at 24V and disengage at 23V. It feels like there isn't enough current to constantly feed the reversing valve causing the value to oscillate on and off.
I have bypassed the thermostat by feeding the 24v directly from the transformer aka the ( red wire ) and the valve works fine; it receives a steady 26V AC and the reversing valve remains active. This leads me to the conclusion that the Nest thermostat is now defective.
What can be done to fix this? As I have read a batch of these Nest thermostats were defective out of the factory and within a year or 2 started to fail. Can this be fixed or is this a warranty issue?
My Specs: Type: Nest Learning Thermostat 3rd Gen
Firmware: 6.2-27 Updated May 3rd
Software Ver: 1.5.38 / 3.1
Model: Backplate-5.4
Serial number: 0##############
Power readings: Battery: 3.822 V Voc: 32.40 V Vin: 32.40 V Lin: 200 mA (C)
My Wiring: Y1 - heat/cool ( Yellow wire ) G - Fan ( Green wire ) OB - Heat Pump ( Orange wire ) W2 Aux - Aux, Heat ( Brown ) C - Common 24V ( Blue wire ) Rh - Power ( Red wire )
I’m sorry for the trouble this has caused you. Let me help you out. To isolate the OB terminal on the base of the Nest Thermostat. Have you tried swapping the G wire to the OB terminal and the OB wire to the G terminal?
That sounds like a plan! Please feel free to let us know how it goes. We'll keep this thread open and wait for your update to ensure that everything will be taken care of.
