New Thermostat wiring to zone control panel - need help

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Old 03-03-07, 10:09 AM
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New Thermostat wiring to zone control panel - need help

Need help with wiring: I have a Mastertrol Mini-Zone 3 (MM3) zone controller from Temp-A-Trol with 2 zones in use. The previous thermostats were round mechanical ones. The master or zone 1 had 6 wires (O1, G1, B1, T6/Y, T5/R, T4/W) and the slave or zone 2 had 3 wires (T6/Y, T5/R, T4/W).

My problem is I cannot figure how to wire the new thermostat to the second zone. I have two new HAI Omnistat RC-90B. In master mode they need R, G, O, C, Y, W, B and in slave mode R, C, Y, W. I have upgraded wiring to both locations so the number of wires is not an issue. A single 24V transformer is used.

To get power to the thermostats: On the master thermostat I connected the C to the 1 on the MM3 which is also connected to the C of the transformer. I also connected the 2 on the MM3 (essentially the load or R from the transformer) to the R on the master thermostat so that this thermostat has 2 wires connected to its R terminal (the load from the transformer and the T5/R). With this configuration and the old thermostat on Zone 2 the system works fine (didn't test the AC cause its 20F outside). The problem is the the second floor slave thermostat. I initially attached the RC-90B with T6/Y, T5/R, T4/W on the MMR going to Y, R, W on the stat. To get power, I did the same thing as on the master RC-90B: I connected C on the stat to the splice which is connected to C on the transformer, C on the master stat, and 1 on the MM3. I added a second wire to the R terminal on the stat which is connected to the R on the other stat, 2 on the MM3, and R on the transformer. When I turn power on to the whole system, the fan on the HVAC starts immediately and then the heating cycle starts. Both stats are powered and in the OFF mode. The MM3 lights do no indicate that it is even heating mode. I'm sure the problem has to do with how I'm powering the stats but I'm not sure what to do. There is little information on MM3. I did get its internal wiring diagram from the Honeywell site but couldn't figure it out. I may need a seperate transformer? Thanks in advance.
 
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Old 03-03-07, 07:37 PM
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Zone thermostat

Sorry, I've never heard of any of the controls you mention. Is this zoning with a warm air system? With that many wires, it almost sounds like a heat pump.
 
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Old 03-04-07, 01:08 AM
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Zone thermostat

Its a single stage forced air system with AC as well. The Zone 1 thermostat has more wires b/c it determine the mode of the system (heat or cool, and fan auto or off). The zone controller only has 3 connections for the each stat in Zone 2 and 3. I think the problem is that the controller is designed to only work with older mechanical stats specifically designed for zoned systems. I may just have to fork out another $200 and upgrade my controller?
 
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Old 03-04-07, 10:52 AM
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Zoned Warm Air

I have yet to see a zoned warm air system that worked right. A single stage warm air furnace is either on or off & when on, produces a fixed number of BTUs per hour. That heat has to go somewhere otherwise the system is going to overheat. This being the case, unless each zone requires the same amount of heat (or nearly so) & the furnace is sized for 1/2 the total load you have to dump heat somewhere. My suggestion is to remove the zoned system & have a separate system installed for each zone. Another option might be a two stage furnace. Sorry, I'll get off my soapbox now.
 
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Old 03-04-07, 12:14 PM
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I agree

I agree. I've been in this house for about 6 months and I don't care much for the zone system. Would have preferred 2 systems instead. The redundancy of two systems is an added benefit in cold climates. My hot surface ignitor fried this las Dec on a Friday evening (I live in MN). Scrambling to find a new one was a pain. Fortunately a nice HVAC service man was willing to sell me off his truck (at only a small markup) since all the supply shops were closed. Thanks for your help.
 
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Old 03-04-07, 05:43 PM
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Smile Problem Solved

Figured this out. I needed two put the thermostats (or at least the zone 2 stat) on a seperate 24V power supply. The zone controller doesn't (I assume because of its internal wiring) allow you to use the same power supply or power steal). I think my original connections was causing the heat relay to close on the zone controller incorrectly. Either way its working now. Future project will to connect the stats to a compute or home automation equipment!
 
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