Thursday 11 February 2021

Mystery Issue That Can't Be Solved

Guys,

I have been having an issue with my furnace for awhile now which can't seem to be solved. Had a furnace service out to review it and he spent 6 hours here trying everything. Below are the facts. Hopefully someone here will be able to help!


- Have a carrier high-efficiency 80k BTU 93% furnace
- Installed a Honeywell RTH9585WF1004 Wi-Fi Smart Thermostat about a year and a half ago
- Home is 1666 sq ft in the metro Detroit area with a finished basement
- Home has always maintained temperature hot or cold

Now for the issue. I noticed a power cycle of my new thermostat which happened every 10-15 minutes while it ran. I did a lot of googling and it seemed that it was the high-temp limit switch tripping. I had a highly recommended heat and cooling service provider come out and below is the list of everything he looked at and tried.

- Saw the high-limit switch was tripping which was causing the power to be cut to the smart thermostat
- Replaced the high-limit with no fix to the issue
- Took out the filter (16x25x5 3M filter) and still tripped
- All vents (return and feed) are completely open
- All dampers are completely open
- The furnace fan was turned up to a higher speed and still tripped
- Everything is clean

He finally tested the pressure before/after the furnace and it seemed that the feed into the furnace was not enough. The suggestion was to add a 12x6 vent right before the filter to attempt to allow more air into the system. Unfortunately, even adding this 12x6 vent AND removing the filter, it STILL trips the limit switch which is killing power to the thermostat.

Basically myself and the technician are out of all ideas and have no idea what the issue is. Anyone on here that has ANY idea would be greatly apricated.


source https://hvac-talk.com/vbb/showthread.php?2226484-Mystery-Issue-That-Can-t-Be-Solved&goto=newpost

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