how to wire Honeywell T-stat TH8320WF


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Old 10-23-14, 09:26 AM
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how to wire Honeywell T-stat TH8320WF

I am trying to change my old Honeywell round T-stat to Honeywell Wi-Fi TH8320WF. got a question about wiring.

Old T-stat only use 2 wires -- R & W. I think it only serve as a temperature feed. Furnace is controlled by zone panel MasterTrol Mark V (model mabs-v-3). There is a rotary switch in the furnace room to switch between Heat-Off-Fan-Cool.

When I change the T-stat, I just wire the R & W into the new T-stat. I also use one extra line as C wire. But it seems that any temperature change made in new T-stat has no impact on the furnace. For example, I put it in heat mode, try to increase to higher temperature. on screen, it shows some info like "auxi heat on". but furnace will not be on at all.

any suggestions?

here are some pictures:

zone control panel
Name:  Zone Controller - 7.jpg
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rotary switch
Name:  Zone Selector - 1.jpg
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T-stat wire
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Name:  Upstairs-Round Honeywell Thermostat-series 20.jpg
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only Red--R & White--W wires are used. I use Green wire as C wire for new T-stat.
 
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Old 10-23-14, 10:04 AM
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Did you go into the installer's setup and set function 170 for the type of heat you have? If not, check pages 5 and 6 to see how to enter the setup menu and set function 170.


https://customer.honeywell.com/resou...69-2733EFS.pdf

The Red wire will be 24V from the transformer
The White wire is for the heat relay
The C wire is the common coming from the low voltage side of the transformer
 

Last edited by firedawgsatx; 10-23-14 at 10:20 AM.
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Old 10-23-14, 12:32 PM
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I was trying to do that. but system setup menu do not have 0170. it has 0165, then the next is 0280. it does not show all those codes between 0165 and 0280.
 
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Old 10-23-14, 01:09 PM
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As shown on page 5, did you press "system" on the left side of thermostat then press the two buttons on either side of the center button at bottom until the menu appears?

I think you are only accessing the limited access menu. See attached diagram to refer to the procedure.
 
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Last edited by firedawgsatx; 10-23-14 at 01:36 PM.
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Old 10-24-14, 12:37 PM
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just solve the problem. it turns out that my zone panel will not support wi-fi version T-stat since it uses C wires. I have to use a non wi-fi version programmable T-stat. Then I connect W-T4, R-T5, Y-T6. it works well now.

I know there is some way to make extra wire for C-wire. just wonder whether I can use that method to create a C wire or not.
 
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Old 10-24-14, 01:26 PM
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Here is my suggestion:

Measure for voltage between the T5 terminal connected to your thermostat R and the 1 and 2 terminals in the 24V 40VA transformer section (circled in white in attached photo). One of those terminals should measure 24V and the other measures 0 Volts. The one that gives you 24V should be able to be used as the C connection for your thermostat.
 
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Old 10-24-14, 10:33 PM
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Thanks for your suggestion. I did measure it before. Volt_1&T4 = 20V, Volt_2&T5 = 20V. I was trying to add extra wire from 2 as C-wire. But as soon as I turn on power, I heard one metal shaking sound which I never heard before. So I shut down power right away. good thing is that everything seems ok now.

I did call Honeywell tech support. Thanks for their great effort. I got a diagram for zone panel.

Name:  Honeywell MasterTrol Mark V model mabs-v-3 Diagram-c_Page_2 - Copy1.jpg
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Name:  Honeywell MasterTrol Mark V model mabs-v-3 Diagram-c_Page_1 - Copy.jpg
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it should help us to confirm that whether we should try that again?
 
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Old 10-25-14, 06:42 AM
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According to the diagram you posted, the 1 and 2 terminals are direct connections to the 24VAC transformer. If you measure across 1 and 2 terminals it will give you the output voltage of the transformer. It should be around 24V. The RC terminal (R on yours) as shown in the bottom diagram of first image is the 24V "hot" side from the transformer. So if you measure between the RC terminal and 1 and RC and 2, whichever gives you a 24V is the terminal you want to connect your C wire for the thermostat. In the second photo it would appear M1 is the common from the transformer terminal labeled as 1. Based on that, I would figure number 1 terminal is the one you would use. But testing, as I suggested. will verify that. The diagrams provided by Honeywell appear to be for a different version than yours and why I suggest the testing.

Don't forget to remove the jumper wire on the thermostat between R and RC (if present) because you have a two-transformer set-up.
 

Last edited by firedawgsatx; 10-25-14 at 08:48 AM.
 

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