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A couple weeks ago our downstairs thermostat started acting strange, kept switching to heat instead of cool, at first we thought the nanny was messing with it. I then saw it was running on battery power, off of ancient batteries, and it was just resetting itself. I replaced the batteries, but then realized it was running on batteries because it wasn't getting power, messed with it a bit and found that the air conditioning wasn't turning on, and couldn't get the fan to turn on either. I know just enough to be dangerous, so tried a manual override to see if the fan would turn on, no go. I've opened up the panels on the furnace to see if anything was odd in there, and it looks like there's a diagnostic LED that is off, which according to the panel means "check power." Outlets on the switch box for the furnace work fine. Anything else I should check, or should I call in a professional?
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Sep 28, 2016 04:29
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| # ¿ May 4, 2024 12:38 |
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kid sinister posted:Just for the record, is the switch on? Yeah, switch is on (I've turned it off an on again). I do have a multimeter, but didn't try checking anything on the inside, I'll see if I can figure out which wires should be 120 volts.
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Sep 28, 2016 05:14
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devicenull posted:Sometimes people put a sensor on the condensate line, so that if it backs up the furnace turns off rather then flooding your house. I think they're usually inline with the thermostat power supply. Yeah, nothing on the condensate line. But I tested what I thought were the hot and neutral wires and it was only showing 1 volt, but then I realized the hot went through the panel detection switch, measured from that connector, and got the full 120 volts. I bypassed the switch and connected the board directly, and same null result from the diagnostic LED. Here's a photo of the board in case it's useful. 
borkencode fucked around with this message at 02:02 on Sep 29, 2016 |
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Sep 29, 2016 01:59
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glynnenstein posted:Is that 5 amp fuse intact? Yep
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Sep 29, 2016 14:33
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literally a fish posted:LV transformer failure? That sounds like it might be promising, I can check tonight, I think it should be that box on the right side there? I think that looked like a transformer. Should have snapped a photo of the circuit diagram too..
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Sep 29, 2016 16:41
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OK, just double checked, and it does look like it's the transformer. 120 volts on one side, 0.001 on the other. Here's the actual transformer.  Tried googling for the model and only found ebay links, can I just replace it with any 120->24 volt transformer?
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Sep 30, 2016 05:46
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kid sinister posted:Any? If you want it to fit the 2 existing screw mounting holes, probably not any. But yeah, that sounds like you need a new transformer. Yeah, alligator clips would have made it a bit easier. I also checked the resistance across the terminals (with the leads unclipped of course) for the 120v side and got an OL.
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Sep 30, 2016 14:47
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Yeah I was checking black/white, and red/light blue.
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Oct 1, 2016 00:24
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Woke up very warm this morning and heard a loud humming coming from the HVAC, not my favorite way to wake up. Blower fan seems to be having a bad time. Worried the fan seized, I opened the unit up checked that the fan still spins (it does). I turned the power back on to hear things up close and everything seemed to kick back on just fine. Couple hours later and the buzz is back, so I go check again. The fan blades are moving very slowly while the unit hums. Capacitor is maybe bad? It's rated 7.5 uf @370v, but multimeter says 7.38, which is within 5%, but maybe just low enough to not work? Anything else I should check?
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Jul 14, 2019 18:34
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Motor did seem slightly warm to the touch, even after sitting idle for a couple hours in my 65 degree basement. Don't have a clamp meter currently (no pun intended), but the motor is embedded in the fan assembly so I can't tell the specs anyway.
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Jul 14, 2019 19:50
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Ran to grainger this morning and bought a new capacitor. Thought it was going to work for about 20 seconds, as the fan started spinning a bit faster before slowing down again. Looks like a new motor is in my future.
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Jul 15, 2019 18:35
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Got the new motor installed and ac is working again, not sure if I’m more excited about it not being 78 degrees in my bedroom, or that I won’t have to go back to grainger for a fourth day in a row.
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Jul 18, 2019 15:51
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My upstairs furnace has been acting a bit wonky for a while now, it seems like it's doing two different things. 1. Cutting off early when heat is still being called for. 2. Not starting at all when heat is called. (Turning it off for a while, then back on gets it to kick back on, then runs until temp set). Last night I was able to short the wires in the furnace, and it ran just fine, making me think it was the thermostat. Today I messed with the thermostat, tightening the connections, replacing the battery, and it came on, but turned off early. So I'm not sure which end is the problem.
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Mar 7, 2020 02:36
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| # ¿ May 4, 2024 12:38 |
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Well, I think I fixed my issue. I was trying to bypass the thermostat and just connecting the wires at that end directly, and the fan worked but nothing happened when I connected up the heat. Looked at the furnace again and while poking around I found that one of the connections coming off the transformer was extremely loose. I tightened it up and everything seems to be working correctly again. Explains why it would work occasionally when I would try and diagnose it, if I bumped the connection back together, but then vibrations from it running would eventually make it fail.
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Mar 8, 2020 04:54
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