Nest 3rd Gen Faults & Failures

TPOW — Thu, 23 Jun 2022 17:31:58 GMT

When I installed my Nest originally I ended up having to change the multi-conductor cable from a 4 to a 5 to get a common for proper battery charging.

Most people don't realize the other problem is that the integrated relays for the (call for heat &2nd stage/cool &2nd stage/humidifier/ & other extra controls) are not very tolerant to voltage drops or spikes. My furnace would try starting & sometimes fail giving a look as if it was cycling, but it was the Nest thermostats integrated relay briefly opening the circuit causing the furnace to restart its start-up sequence. I found this by connecting 2 Fluke multimeters, one to the incoming power & common wires, & the 2nd to the call for heat & common wires. My HVAC uses a 24vac transformer for its control voltage. The incoming voltage shows a steady 27.34vac then the call for heat shows the same but then drops out 25.47vac on the RMS, but when looked at on an oscilloscope shows a complete dropout. To fix this I purchased some high tolerance Finder brand relays for about $50 & controlled them with the Nest & controlled the HVAC via the Finder relays.

Re: Nest 3rd Gen Faults & Failures

TPOW — Thu, 23 Jun 2022 17:39:38 GMT

Re: Nest 3rd Gen Faults & Failures

TPOW — Thu, 23 Jun 2022 17:41:33 GMT

Re: Nest 3rd Gen Faults & Failures

Brad — Wed, 17 Aug 2022 18:22:15 GMT

Hey there,

In an attempt to keep content in these forums fresh, we'll be locking and closing this thread. If you still need assistance with this issue, feel free to start a new thread. Thank you for your understanding.

Best regards,
Brad

topic Re: Nest 3rd Gen Faults & Failures in Nest Thermostats

Nest 3rd Gen Faults & Failures

Re: Nest 3rd Gen Faults & Failures

Re: Nest 3rd Gen Faults & Failures

Re: Nest 3rd Gen Faults & Failures