Make-Up Air Damper and Interlock
| What it is | A powered damper in a separate supply duct, wired to open whenever the hood runs. |
|---|---|
| Where it sits | In a separate supply duct, with an interlock back to the hood |
| How it fails | Stays shut when the hood runs, so the hood cannot pull |
| Checked with | The interlock signal first, then the damper motor itself |
| Price | Quoted after the $89 visit |
Air has to come in as well as go out
A hood does not make air; it moves it. Everything the blower sends up the duct has to be replaced from somewhere, and in a tightly built house there is nowhere for it to come from. The blower then works against the house itself, and the pull at the cooktop drops away even though nothing has broken. Where a kitchen was fitted with a supply duct, this damper is the door on it.
The interlock, and what it is waiting for
The damper is not on a switch of its own. It waits for a signal that the hood has started — a contact closed at the hood or at its control — and opens on that signal alone. So a damper in perfect order can sit shut all evening, because nothing told it the hood had started. The signal is the first thing measured.
A damper that never opens
Three things show up. The interlock wiring, run at the time of the remodel and never touched since. The damper motor, which has an easier life than a blower but does eventually stop. And a blade stiff in its frame after years of sitting in one position. Which of the three it is decides who finishes the job, and that is settled on the visit. Wolf Repair Los Angeles, (310) 626-4008.
What putting it right costs
Only the damper, its motor and the interlock signal are ours. The supply duct itself, and anything that heats or tempers the incoming air, is heating and ventilating work that we hand on rather than quote.
A flat $89 buys the call-out and a full diagnosis, and that $89 is deducted from the repair once you have approved it.
Follow-ups
The hood has slowly gone weak over the years. Could this be why?
It can be, particularly after windows or doors have been replaced and the house has been sealed up. Nothing in the hood has changed; the supply of replacement air has. The way to tell is to crack a window near the kitchen and run the hood again. If the pull comes back, that is your answer.
Do I need make-up air at all if I do not have it now?
That is a question for whoever sized the kitchen ventilation, not one to settle over the phone. Wolf Repair Los Angeles works on the hood, the damper and the interlock between them; deciding whether a supply duct belongs in your house is heating and ventilating design, and we will say so plainly.