HRV Furnace Interlock issue

[1patfan]

Hi

Recently installed a Venmar HRV Solo 2.0 and connected the HRV's intergrated interlock relay to furnaces R&G terminal block (Amana Air Command 90 gas). The HRV does activate the blower motor as it is supposed to when the HRV runs.

The Problem is that when the HRV is running and energizing these terminals, and the thermostat calls for heat the furnace will not run. (Thermostat set in auto fan mode).

Howerver, If i set the thermostat fan mode from <auto> to <on>(continuous) the HRV will run nomally and the furnace will run normally if called and slows the blower speed automatically to coincide with the preset heat blower speed setting.

The thermostat is an aprilaire 8334 1 heat/1 cool digital.

Would like to remedy so that blower motor runs when hrv is operating (not continuous), but obivously need to have heat when the thermostat calls.

any help would be appreciated, dont know if this is a furnace or thermostat issue.

thanks!

[Black Adder]

Is the HRV sending 24v to the furnace? Should be no voltage coming from HRV. Try disconnecting the HRV and put a jumper wire accross R and G on the furnace board and see if the heating will operate. If it does then the problem is with the interlock switch of the HRV if it doesn't then you have a problem with the furnace board.

[1patfan]

No there is no voltage from the HRV it is closing the R&G terminals and is in fact activating the blower motor like it is supposed to (in effect jumping the terminals). The furnace will not operate only if the thermostat is set to auto mode, it will work with the hrv running when the thermostat fan is set to fan continuous on mode, thats what is puzzling. I

in fact if the hrv is running, and the furnace and blower motor are going, if i switch the thermostat to AUTO mode the furnace will shut down and the fan speed will change to fan only mode (circulator blower is energized on cool speed, "it speeds up").

[1patfan]

I had to wind up disconnecting the G wire at the thermostat now the heat works fine and the hrv is interlocked with the furnace blower. This furnace does not need the G wire to run the blower for heat/ac, does it automatically when W&Y are closed w/R. Only needs it from the thermostat to run the fan manually, which i now do with the adjacent HRV control w/fresh air. Since the HRV closes R&G to run the fan only mode, it must have been interfering with the thermostats auto mode functionality when R&G was closed by the HRV. Perhaps a different thermostat brand would have worked better?

[Black Adder]

Glad you solved your problem, sorry didn't think that wire to g on tstat would be causing a problem.

[markwolf]

Sounds like you have a feedback issue with the thermostat.You could try an isolation relay to eliminate the feedback that way the fan on option could still be used on the subbase.