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Old 01-19-2009, 03:29 PM   #1
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Crashing Visionpro TH8300


Hello,

I have had a Honeywell TH8320U1008 installed on a multi-fuel heat pump with natural gas as backup. It works OK, cooling, heat with heat pump and automatically goes to fossil fuel when very cold.

Problem is that every now and then the display is scrambled or frozen. Sometimes can go a while before crashing sometimes several times a day. I am wondering if there is something about the hook-up that could cause the thermostat to crash?

Attached is a PDF schematic of the hook-up and programming settings

Thanks in advance,

Mark
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File Type: pdf HVAC Hook Up.pdf (14.7 KB, 164 views)

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Old 01-19-2009, 04:22 PM   #2
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Nothing I can think of. Sounds like a problem with the stat. Is this a new system or has always happened or a new problem with a system that has been in place a wile?

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Old 01-19-2009, 04:31 PM   #3
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Hello John,

Thanks for looking.

It was all installed new about two years ago. The first TStat lasted about a year then began to crash. Purchased a second identical model but it also crashed. Warrantied the first getting yet a third new TStat and it crashes too.

This is getting to be an expensive sport!

It appears to share 24V AC from the furnace but I am not sure which lead provides the ground or common connection.

TStat has batteries installed that are in good shape as well.

Mark
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Old 01-19-2009, 05:09 PM   #4
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You may want to check the warranty on the stat I think it may have a factory 5 year warranty.
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Old 01-19-2009, 06:39 PM   #5
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Yes, has a warranty. The shop says that these very rarely fail. So I am thinking that since three in a row have failed perhaps something else causing them to fail.

Something I wonder about is in the install manual very first thing it says for 24VAC primary power connect the common side of the transformer to the C terminal. This one the C terminal is not hooked up.

Then later in the terminal letter designations for C it says "Common wire from secondary side of the cooling transformer" or "Common wire from secondary side of the cooling transformer (if 2 transformers)"

This is confusing as it seems like there is a need for the common to be connected to complete the 24V AC circuit. Are any of the other wires used as a return?
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File Type: pdf HVAC Hook Up.pdf (14.7 KB, 93 views)
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Old 01-19-2009, 07:16 PM   #6
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Crashing Visionpro TH8300


You said your system is 2 yrs old. Did they replace the t-stat wire from the furnace to the t-stat, also from furnace to heat pump. It seems to me that you are getting back feed from some where or a skinned wire that touches with vibration causing the t-stat to go crazy on you.

I would have hooked up common if you have enough wires to the t-stat. It's not necessary to have common, but it will save you on batteries.
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Old 01-19-2009, 07:37 PM   #7
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Crashing Visionpro TH8300


Sorry I left that out, new wires new furnace, new heat pump. Everything new.

I took the batteries out of the stat to see if it would work on the furnace 24V power. It didn't.

Located and attached a wire to the common 24V lug on the transformer and then used the "extra" blue wire between the furnace and the stat attaching it to the C stat terminal. Checked voltage at the stat between C and R (24V) and replugged w/o batteries. Display now works w/o batteries.

Added benefit - there is a bright red lamp when operating on emergency power that have never seen before. Maybe does not glow when on battery only.

So it seems for two years it has been operating on battery only.

Have to wait and see if it solves the frozen screen problem. . .

Keeping fingers crossed.

Thanks for your help.

Mark
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Old 01-19-2009, 09:43 PM   #8
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your cooling TR is the main transformer in the air handler side of the same system.that C is the other side of the TR as stated but they are calling for a true 24Vs at the subbase to power the new stat...you might be failing due to a feed back powering up but not enough to swing the systems.older stats always worked off that back feed thru either Y1,W1,G.....etc.then the electronic stats started showing up and with out that C common from the system TR it would light up,take setpoints,and just sit hook it up whats the worst that can happen
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Old 01-23-2009, 11:20 AM   #9
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Hello,

It has been several days since adding the C to common of the 24V TR.

No problems so far.

Thanks to all.

Mark
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Old 01-23-2009, 01:11 PM   #10
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Crashing Visionpro TH8300


Thats great to here. Thanks for letting us know.

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