Wiring of blower GMP100-5

Old 11-14-20, 05:04 PM
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Wiring of blower GMP100-5

I installed a par of Ecobee thermostats in my house, and I have run into an issue. Sometimes the power to the Ecobees just cuts out in during a heat cycle. Not every time, but frequently. When this happens the fan is runs for a couple of minutes longer before the heater shuts off. My guess is that the heat cuts out at the same time the power to the ecobees is cut. The systems is in the attic and not easily accessible, so I'm unable to confirm.

My review of this forum has indicated that this is likely happening when a temperature sensor detects a overheating situation. This is due to a cracked exchanger or insufficient flow from the fan. Any other possibilities?

Based on this I started to explore the situation. After determining my system was a GMP100-5 I found some unit specific info on how to increase blower speed to see if that could fix the issue.

This is where the fun starts. The red and blue wire from the blower are not connected to anything, The COOL lug has a splitter one for the black wire and the other to connect the COOL and HEAT lug. This is not even close to the wiring diagram Red - HEAT Blue - COOL Black - M1.

Is this a safe way to run this system? Why would it be done this way?

In the picture you can see the cut blue wire with the wire nut. The red is similar. The 2 cut wires are then connected with a wire nut to tie the 2 lugs on the board together.

The ecobees are unlikely the issue. This was probably happening with the old thermostats, it is just that those did not rely on power from the HVAC system.

Old 11-14-20, 05:25 PM
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Welcome to the forums.

That kluged wiring is so that cooling and heating are both running at high speed.
You need to confirm what the actual problem is.
If it's a cracked heat exchanger.... that MUST be addressed..... typically by replacing the furnace.

You need to check the heat rise thru the furnace. That requires measuring the discharge temperature and the return temperature and subtracting them. The max heat rise is posted on the ID sticker inside on the sidewall near the burner.

If that furnace hasn't been professionally serviced and checked in the last few years.... have it done.

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