I Think I Messed Up a Honeywell Control System

Old 07-17-14, 10:45 AM
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I Think I Messed Up a Honeywell Control System

Hi All,

I had a Honeywell VisionPro IAQ thermostat (YTH9421C) working with a THM5421C Equipment Interface Module controlling a Trane variable, two-speed HVAC system.

I replaced the VisionPro IAQ Thermostat with a Honeywell Wi-Fi Thermostat (I think the RTH6580). I bypassed the EIM and wired the Wi-Fi Thermostat directly to the furnace.

Everything seems to work fine EXCEPT at various times in the cooling mode both the blower in the furnace and the fan on the outside unit kick into really high speed. This doesn't seen to be a problem for the furnace blower but whenever it kicks into high speed, the outside unit rattles really loud.

I am not sure it the HVAC unit started doing this as soon as I replaced the thermostat but I think so.

Do I need to see if I can find the old Vision Pro (or get a new one) and put it back on or can I adjust the setup of the WiFi thermostat?

Old 07-17-14, 07:28 PM
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If your system continues to blow cold air when this noise occurs it was probably already making this noise before you replaced the stat.

It would still be a good idea to have your system serviced including measuring the caps, compressor and fan amperage, superheat, subcool, a visual inspection of the wire connections in the unit, rinsing the condenser, checking the delta t, inspecting the indoor coil, blowing the drain and putting some pan tablets in the primary drain pan.

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