I recently bought a home with a dual HVAC system (older Carrier & newer Bryant furnaces). It also has Aprilair humidifiers on each furnacea and a Venmar HVR.
The Bryant furnace is for the main floor and was controlled by a Bryant Connex thermostat located next to the Venmar control. One of the reasons I wanted to switch to the Ecobee was to connect the HVR to the thermostat and get rid of the extra controller on the wall.
I swapped out the thermostat controlling the Carrier system without issue. When I went to do the same for the Bryant system, I discovered it only used 4 of the 5 wires (Red, Green, Yellow & White; the Blue wire was not connected to anything).
On the Ecobee I connected R to Rc, G to G, Y to Y1, W to W1 and the Blue wire to C. I connected the HVR red wire to the ACC- & the white wire to the ACC+.
On the furnace control board I connected the Blue wire to the Comm terminal. There were 2 other wires already connected to Comm, but I did not trace them.
Everything seemed to be working as designed, however soon the Bryant 3 amp fuse blew. I replaced it, only to have it blow again.
What could be causing the problem?
The AC and humidifier would be the other 2 wires on the C terminal and there should not be a problem with adding the Ecobee C wire. Are there low voltage wires connected between the HRV and furnace?