Is my thermostat broken, or something else?
October 28, 2024 2:35 PM Subscribe
We have a ZONE950AC52ZA thermostat and a DHMC100ACV4VA...system. We bought this house 1.5 years ago and haven't had an issue until recently when the thermostat went black. As soon as I can afford to I will contact a professional, but for now, I'm hoping to at least exhaust things a semi-handy person can do themselves. Here are the steps I have taken so far.
1. Checked the breaker. It's was fine.'
2. Took face part of the thermostat off the wall and re-inserted it. Still nothing.
3. Checked the voltage with the multimeter. It hovers around 12V.
4. Checked the wet trigger kill switch thingy that everyone recommends on the internet, it's not wet, that doesn't seem to be the issue.
5. Opened up the blower door to get to the user interface display. Unit test works, goes through both stages.
6. Looked at last 4 faults. It lists sys comm crc.
7. Checked the voltage of D&B on the IFC, also 12V.
8. Started going rogue and decided we needed AC because it was going to be a high of 100 so bought a cheap thermostat from Ace (ATX100E-A04) wired it up, then blew a fuse on the IFC.
9. Replaced the fuse on the IFC, now have a box of fuses to last a lifetime
10. Now fault list is sys comm crc, check fuses, and sys comm crc.
Is there any way to test if the thermostat is the problem before I order a replacement off of ebay? Like alligator clip some batteries or some nonsense to see if it will even turn on? Other members of the household says the thermostat has had spells of going black before but it would come back on.
Thank you!
1. Checked the breaker. It's was fine.'
2. Took face part of the thermostat off the wall and re-inserted it. Still nothing.
3. Checked the voltage with the multimeter. It hovers around 12V.
4. Checked the wet trigger kill switch thingy that everyone recommends on the internet, it's not wet, that doesn't seem to be the issue.
5. Opened up the blower door to get to the user interface display. Unit test works, goes through both stages.
6. Looked at last 4 faults. It lists sys comm crc.
7. Checked the voltage of D&B on the IFC, also 12V.
8. Started going rogue and decided we needed AC because it was going to be a high of 100 so bought a cheap thermostat from Ace (ATX100E-A04) wired it up, then blew a fuse on the IFC.
9. Replaced the fuse on the IFC, now have a box of fuses to last a lifetime
10. Now fault list is sys comm crc, check fuses, and sys comm crc.
Is there any way to test if the thermostat is the problem before I order a replacement off of ebay? Like alligator clip some batteries or some nonsense to see if it will even turn on? Other members of the household says the thermostat has had spells of going black before but it would come back on.
Thank you!
When you say you’re getting 12 volts, are you measuring AC voltage across the hot and common wire coming from the unit? Control voltage for units is basically universally 24 volts nominal AC (more typically around 26).
posted by HVACDC_Bag at 5:11 PM on October 28
posted by HVACDC_Bag at 5:11 PM on October 28
How's the internal wiring look -- anything visibly loose? Any capacitors that look like their top popped, or have smudge around them? Has anyone hung a picture lately where the thermostat wire might run, or added something to the electrical circuit that feeds the furnace?
The manual lists SYS COMM CRC having three possible meanings on page 55. depending on the second LED: "Inducer Motor unrecognized response," " Blower Motor unrecognized response," or "COMM System unrecognized response" -- which suggest a lost connection to a component, or garbled data on the line.
But farther down the page it also suggests "Loss of heat/cool demand" or "Loss of clock signal"; and yeah, that makes me think that there thermostat isn't talking to the furnace, or that the wiring has a fault.
posted by wenestvedt at 6:19 AM on October 29
The manual lists SYS COMM CRC having three possible meanings on page 55. depending on the second LED: "Inducer Motor unrecognized response," " Blower Motor unrecognized response," or "COMM System unrecognized response" -- which suggest a lost connection to a component, or garbled data on the line.
But farther down the page it also suggests "Loss of heat/cool demand" or "Loss of clock signal"; and yeah, that makes me think that there thermostat isn't talking to the furnace, or that the wiring has a fault.
posted by wenestvedt at 6:19 AM on October 29
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posted by How much is that froggie in the window at 2:57 PM on October 28 [1 favorite]