Verifying Setup For Old McQuay Unit with Honeywell Thermostat

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Old 12-15-19, 05:14 PM
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Verifying Setup For Old McQuay Unit with Honeywell Thermostat

Hey guys - I've got some questions with regards to a thermostat setup and wanted to get advice on any potential issues. There are a lot of postings on this site for the RTH3100C, but I haven't been able to find an answer to these. I've attached pictures of the new wiring below (no longer have the photo of the old thermostat wiring).

Thermostat: Honeywell RTH3100C - Manual (cycle settings are 3/3)
Unit: McQuay Water Source Heat Pump PTAC W-WMS-2-019-E-Z / September 2006 - Catalog
Installed: Apartment building with water coming from roof reservoir

1. The heat works great but only comes on when in emergency heat mode even though there is nothing wired to "E". In standard heat, the compressor doesn't kick on at all, and on one of our 3 units, cold air comes out. Is this because I don't have a jumper between E and AUX, or is there another potential issue like the thermostat not being compatible with the unit? If it needs a jumper, what is the main reason for the jumper in this case?
2. There is a light layer of gray/black residue (visible in photo below) on the inside of the unit creating little swirly shapes. Is it more likely to be dust or a potential electrical wiring issue?
3. The thermostat first starts with "Em - Heat On" with the fan running but no heat. After a few minutes, it changes to "Em Aux - Heat On" which is when the actual heat kicks in. Why does the Honeywell thermostat start the fan first and then the heat? Or is this a side effect of using the unit in emergency heat mode? I've attached pictures of the thermostat display in both modes

Thanks,
Jeremy

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Last edited by PJmax; 12-15-19 at 07:07 PM. Reason: resized pictures
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Old 12-15-19, 07:19 PM
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Welcome to the forums.

That was a thermostat you decided to install..... correct ?
From what I'm reading..... that's not the correct stat for your equipment.
Heat pump systems use change over valves.

It would have been ideal to know the wiring on the old thermostat and what it was.
 
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Old 12-17-19, 10:35 PM
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It looks like you cannot use that heat pump thermostat for your unit.

The terminals that you will use include G, Y, W, R and C.

A heat pump thermostat will energize Y for heating or cooling demand but you only want Y for cooling according to the manual that you posted.

You want a conventional thermostat configured for electric heat.
 
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Old 12-26-19, 11:16 AM
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Thanks guys. I was able to get pictures of one of the old thermostats from elsewhere in the building as well as a new one that was installed next to it. The new one is wired to G, Y, W, R, C like you suggested, so I think I'll go with the same thermostat model.

It's also interesting that this thermostat had the same gray dust inside. Could that be due to old wiring or likely just dust getting trapped inside the unit?
 
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Old 12-26-19, 09:25 PM
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I wonder if return air is pulling through the stat.

A "common return air" application or a stat mounted by the return air chase would cause some dust here.
 
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