Problem with home HVAC. Need advice.

hey guys,

We have 2 HVAC units (with heat pumps) in our house (only 5 years old) and we are having the same issue with both of them. Both units will heat and cool the house just fine. However, when the heat or cold cycle is complete, the outside fans will shut off, but the inside blowers will not shut off properly. Sometimes, the blowers will stay on for hours or they will intermittently turn off and turn back on. and sometimes they will turn off like they are supposed to

We had a local HVAC company come out to inspect the units (and of course this issue didnt happen when they were out here) and they said they everything checks out and the units are running properly. They guy thought that maybe the issue was with the thermostats. He suggested removing the thermostat from the wall when this happens and seeing if the blower shuts off. He said that it should. However, when this happened again, I removed the thermostat from the wall and the blower kept running.

What does this sound like to you? Have you ever seen this problem before? Any suggestions?

Thanks,

 

Hmmm. When I upgraded to a nest thermostat, it seems to have a energy saving feature that turns off the heat/cool and just runs the fan (blower) to save energy, but for hours...no way.

I’m no expert but maybe look into the limit thermostat inside the unit, that’s what controls when those blowers turn off (I think). I had an issue last year where I purchased too good of a filter and it was not allowing enough air to pass thru, got too hot in my furnace and burnt that limit thermostat out. Blower would run intermittently and such but never for hours.

 

Just curious; does your system (both) have humidifiers?

 

Probably a fan relay sticking on the circuit board. Most units have a setting on the board to determine the length of time that the fan will run after the outdoor unit shuts off . This is to extract the most efficiency from the coil before the fan shuts off. Usually 30,60 ,90 seconds. If it runs longer it is a bad relay or thermostat issue. Some thermostats have the same settings in them . Yours sounds intermittent which leads me to think a bad fan relay.

 

no

 

Process of elimination... I agree with Yota-Man.

 

I agree that it sounds like a relay. Find the relay. When it hangs, check the voltage to the relay that controls closure. If it doesn't have voltage and yet it is still closed. Then it is the relay. I'm assuming its is not naturally closed. Basic relay troubleshooting of HVAC found here...

https://www.youtube.com/watch?v=RKfRh9f326A

 

Air handlers are supposed to continue running after the thermostat has turned off the AC or furnace to squeeze every last BTU of heat or cooling out of the heat exchanger or expansion coil. Extended running beyond several minutes is wrong...UNLESS...you have one of those new super efficient systems with variable speed blowers, variable speed compressors, and burners. The most efficient systems now run the air handler constantly at low speed for ventilation.

I doubt the intentional delay is built into the thermostat...the simplest thermostats are a bi-metallic coil and mercury switch. I have a hunch the AC/furnace control board has a timing relay built into it and it's sticking closed.

 

thanks for all the advice, guys.

 

Yep, and my fan will come on before heat coils or AC compressor

 

so, i had the HVAC guy out tonight and, luckily, the blower was running while the thermostat was off (it has been running for 4 days non-stop) and he was able to diagnose the issue. he said that it is a bad blower module. i assume this is the "relay" that you guys were talking about.



he quoted me $650 installed for the blower module ($140 for labor, $510 for the part). that seems crazy to me - $140 for 10 minutes of work? wtf? but its one of those things that i don't want to mess up. screwing up could cost a whole lot more. anyway, he ordered the part and put everything back together. so, blower will run all weekend until the part comes in on Monday.

Thanks for all the feedback, guys.

 

Oooo, labor is labor, everywhere has different prices for labor, but that is way to much to pay for a module.

 

Seems like more than 10 minutes of work. He drove to your house, removed the blower, removed the module, replaced the module, replaced the blower, and ordered the part. On Monday he will go get part and repeat the whole sequence.

 

I have a 10 year warranty on parts atleast....might want to check on that

 

damn..who need a fancy degree when you can get paid $140 /10 min for removing a blower

 

When I consider all existential factors $140 for labor sounds right.

 

yeah, we should have had a 10 year warranty on the systems, but the original owner never registered them with the manufacturer so we only got 5 year warranties on them; which expired in august of 2019. total BS if you ask me.