From the counter: a real question from a contractor, and how we answered it.
The question
A contractor called with a fresh air job that needed three things to happen in order:
- The fresh air damper powers open.
- The damper proves it is fully open.
- Only then does a 120 Vac fan start.
It is a common sequence on ventilation jobs where running a fan against a closed damper would stall the airflow or damage the fan. The question was which Hoyme parts do it most simply, given there was no 24 Vac supply at the damper location.
Option 1: 24 Vac damper with a proving relay adaptor
- HAC-0810-SPO: 8 inch, 24 Vac power open HAC damper with an end switch that proves the blade is open.
- ADP-1102-TPX: interface relay adaptor that waits for the end switch before it starts the fan.
- A 24 Vac transformer of at least 5 VA, since there was no furnace transformer to borrow from.
The advantage of this option is that the 120 Vac fan load never passes through the damper's end switch. The relay adaptor carries it. The trade-off is one more component to mount: the external transformer.
Option 2: a 120 Vac damper that proves and passes power
- HAC-0812-SPO: 8 inch, 120 Vac power open fresh air damper with an end switch and a built-in transformer.
Here 120 Vac opens the damper, and once the damper proves open, power passes through the end switch to start the fan. There is no separate transformer and no relay box, so it is the simpler install.
How to choose
Both options do the job. We suggested the contractor check with the electrician doing the hookup, since the choice comes down to wiring preference. Option 1 runs less 120 Vac cable and uses light 18 gauge thermostat wire to the relay box and transformer. Option 2 has fewer parts but brings line voltage to the damper.
Wiring for the ADP-1102-TPX is shown in its installation instructions and colour wiring diagram 12B, both in the Technical Library.
Have a similar job?
Call free technical support at 1-800-661-7382 with the duct size, the fan voltage and what power is available at the damper, and we will put together the part numbers with you.