HVAC- fan constant running

chiefjason

chiefjason

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Fan/blower is always blowing even when AC is not running. Great when it's warm. Probably not so great as it cools off. Tried to turn it off and back on at the thermostat. No good. Have not tried shutting it down at the breaker.

Some google fu says fan relay bad as the easiest looking solution. Then wiring or thermostat problem. Anything else to look at? Probably poke around with it a bit tomorrow or Saturday.

And I do know how to throw the breaker and disconnect the units before working on them. But I have to learn the small stuff as it breaks. lol

@jjwestbrook
 
Check the condensate safety switch. It could be bad or...
It's good and the condensate is not draining (pump bad, pipe clogged, etc).
 
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Mine was doing this about a year ago. There was a little circuit board built into the motor that went bad. Unfortunately could not buy them separately.
 
jjwestbrook said:
Start with the basics. On your thermostat there is a switch or setting on some digital stats they says "on " or " auto" make sure this is in auto
If thatbis in auto then next I would look at fan relay or fan control board .
Click to expand...

Yeah, it's on auto. Looks like I'll be digging around tomorrow.

Thanks for the info everyone. Gives me some more things to look into.
 
Look in the drain pipe for a float switch, it will have two wires going to it. The top lifts off, if it is full of water you have a drain issue.
 
Dug around for a bit. No water in the overflow tray on the floor. No residual water under the coils in the air handler. Switch seems to be functional. Disconnected the unit and looked inside.

I replaced the start capacitor a while back. But it's a bit dirty. I took some pics that I'll post below. The top board does look to have some brown discoloration on the lower right corner, possible burn/short. One connection on the fan was a bit loose which I tightened. The rest of the connections seemed fine. Took lots of pics of model number info. I have a good local spot as long as they can get them.

On the pics below, so I don't sound like an idiot, what am I looking at? Assuming the fan relay is the bottom and fan board is the top.
 
Board?

3F60A29D-1933-42C3-8CBE-24F03C6E4AD9.jpeg


Relay? Fuse was fine.

D07BDD48-043C-4B40-97D2-11CC2EC3918F.jpeg



Possible burn on board.

BC0F842C-55E1-44A5-A7AA-E4E141EE2A32.jpeg
 
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The first photo shows a relay (Zettler AZ2100-1A-12DEF) which should be easy to find even on Amazon. The second photo shows a transformer.

Amazon has a 2-pack that calls it Trane Fan Blower Motor relay. If you don't need two you can buy a single relay for less than $5.
Amazon product ASIN B0B5DGPZ4L
 
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Off hand, I think the “posible burn“ I browning from heat.if the solder joints look good and the traces (likely underneath the brown spot) are ok, it’s just carrying some current. Given that it is near connections for pink wires on the secondary of the xformer, I suspect it may be an AC to DC rectifier circuit, aka power supply. That the devices between them are installed vertically suggests it was for heat dissipation.

My money is on fused relay. Worth trying. Especially this time of year when neither AC nor heat are mandatory. Worst case scenario, let the air handler fan run and circulate air.
 
Pack72 said:
The first photo shows a relay (Zettler AZ2100-1A-12DEF) which should be easy to find even on Amazon. The second photo shows a transformer.

Amazon has a 2-pack that calls it Trane Fan Blower Motor relay. If you don't need two you can buy a single relay for less than $5.
Amazon product ASIN B0B5DGPZ4L
Click to expand...

Ok. Just to be sure and satisfy my curiosity.

Black box on first pic is relay.

Second pic is transformer.

So is the relay mounted to the fan control board then?

FYI, this unit is 17 years old. If I can keep it going myself I’m all for it. If it comes to paying someone to do anything over $500 I’m just looking at putting that towards a new unit. This one is on borrowed time but a cheap fix is fine.
 
Resistors R1 and R2 could be undersized not in value but wattage rating and that makes them run warmer and can discolor the PC board,
 
chiefjason said:
Ok. Just to be sure and satisfy my curiosity.

Black box on first pic is relay.

Second pic is transformer.

So is the relay mounted to the fan control board then?

FYI, this unit is 17 years old. If I can keep it going myself I’m all for it. If it comes to paying someone to do anything over $500 I’m just looking at putting that towards a new unit. This one is on borrowed time but a cheap fix is fine.
Click to expand...
Here's a photo of the underside of the relay. I believe all of those pins go through holes on the circuit board and are soldered. It shouldn't be too difficult to (1) determine if the relay is bad, and (2) replace it if it is. Step one is to determine which two terminals the relay switches. There should be continuity between those terminals only when the relay is activated (i.e., only when the circuit applies 12v to the coil of the relay). If there is continuity when the relay is not activated (like when you have shut off power to the system) then the relay's internal contacts are probably fused together. You can check this without removing the relay, once you determine which two terminals control the fan. Unplug the two wires that are connected to those terminals and check for continuity using a multimeter.
412fqqz0rSL._AC_SY580_.jpg
 
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Looks something like the relay that made our dryer not work.
 
rdinatal said:
Check the condensate safety switch. It could be bad or...
It's good and the condensate is not draining (pump bad, pipe clogged, etc).
Click to expand...


It was the relay. Found a relay on the board at the local electrical place. $58 for the relay already mounted to the board. So it was all plug and play. Maye 20 minutes to gather up all my stuff, tear it down, label everything, remove, install, hook it up, and close it up. HVAC just shut off from the first on cycle since replacing it, a few minutes later the fan kicked off. Looks like we are GTG.

Thanks to everyone for the info, ideas, and help. This place is as good as youtube and a lot easier to navigate. You guys are awesome!
 
Good find guys! It's harder to diagnose when something won't quit working, than when it won't work at all. Lol.
 
I run my fan 50 minutes out of 60 by choice. It equalizes the upstairs and downstairs temperatures and moves the air through the filter.
 
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