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Fan compartment safety switch: this article describes the door interlock safety switch found on air handlers used in both air conditioning and heating furnaces. We explain how the blower door safety switch works, how it is tested, installed, and wired.
In forced warm air furnaces as well as air conditioning and heat pump system air handlers the indoor air handler's blower compartment houses a fan, usually a round squirrel cage fan and electric motor (to operate the fan) which moves air from the return air plenum on towards the cooling or heating coil.
An access door to the blower compartment should have a blower door interlock switch - also referred to as a blower door safety switch - a safety device which will prevent the blower from operating if the door is opened (see below).
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Blower compartment door switch: an air handler blower compartment access door switch is present on newer units, and can
be seen as a button or switch which is depressed when the blower compartment door or cover is properly in place.
This switch shuts off the blower fan as a safety control if the door is opened. If your air conditioner won't run and someone has been fooling with it, be double sure that the blower compartment door is properly closed and that the interlock switch sensor button or lever is properly depressed to convey that fact to the system. Quoting Trane's typical equipment instructions:
The blower door safety switch will prevent or terminate furnace operation when the blower door is removed
Shown at above left, an Armstrong interlock furnace door safety switch, distributed by American HVACparts.com. The steel bracket is used to secure the blower compartment door switch such that when the door is properly closed and secured the button is depressed, permitting electrical power to flow to the blower motor.
Above is an illustration of a Carrier® blower door safety switch used on many Carrier air handlers.
This blower door safety switch # HR54ZA006 fits Carrier air handlers and is widely distributed including by SupplyHouse.com Tel: 1-888-757-4774 in the U.S.
Many air handlers of more than one manufacturer may accept the same air handler door switch. Often the same OEM interlock door switch will fit Bryant, Carrier, and Payne equipment using 115/120V 2-wire installations.
At below-left is a Trane furnace door safety switch for Trane equipment # DRS652132B (about $35. U.S) that replaces blower door switch part numbers SWT01254, CARSWT1254 used in American Standard Trane HVAC equipment.
A virtually identical switch (above right) is sold for BDP Carrier, # HR54ZA101, AR54ZA100, HR54ZA100, CARHR54ZA101 and fits many Bryant, Carrier and Payne air handlers.
1 Nov 2014 Anonymous said:
on the air handler door safety switch , would like to know what volts is supplying the switch and where thanks.
Usually a furnace or air handler blower door safety switch carries 120 volts.
Watch out: for dangerous shock hazards. Be sure all power to equipment is off before touching any switches, wiring, etc. When power must be turned on to perform an electrical test, for example for the presence of voltage, do not attempt such testing yourself unless you are properly trained in safe procedures and know how to make safe use of your test equipment.
See DMMs VOMs SAFE USE OF
A typical 120V door interlock safety switch should conduct power (and show 115-120V across the switch) when electrical power to the air handler or furnace is ON and the door is latched (or the switch button is depressed).
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Shown at left is an excerpt from a Trane® gas fired furnace. Our red rectangle shows the location of the blower door switch on the wiring diagram. Be sure to refer to the proper wiring diagram for your own HVAC equipment. - "TUX-D-2 Up flow/Horizontal Left Downflow/Horizontal Right Condensing Direct Vent Gas Fired Furnace XR90 TUX040-series, single-stage fan assisted combustion system" from Trane, retrieved 11/5/2014, original source: http://www.trane.com/commercial/uploads/pdf/1112/tux_c.pdf
Hook-up is so simple that you might simply use the existing door switch wiring, connecting it to the replacement switch.
The switch is connected in series between a relay in the air handler that operates the blower fan and a terminal on a control circuit board in the unit. The switch is not powered independently. It's power comes through the circuit board.
You'll be able to see this by following wires from the blower door safety switch back into the air handler.
But if your air handler or furnace is an older one that did not include a door interlock safety switch you'll want to wire the switch so that it interrupts power to the blower fan.
Replacement blower door switches are easily obtained for your air handler by brand and model via your local HVAC supplier, from the manufacturer, or often online. Some safety switches will work properly on several air handler brands and models.
I add that the blower door switch is an important safety feature that helps avoid chock or chopped-off fingers or worse. Be sure that your replacement switch is properly mounted so as to be reliably operated by the blower compartment door(s) - the switch opens- cuts off power - when the door is opened, and is depressed in to close and permit power to the blower when the door is properly closed.
2016/08/14 Linda said:
Where is the blower door located at ?
At AIR HANDLER BLOWER DOORS I've added some photos and created this article to help you see what you're looking for when you need to find the blower compartment access door or cover on an air handler.
Continue reading at CONTROLS & SWITCHES, A/C - HEAT PUMP or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.
Or see AIR CONDITIONER WON'T START
Or see AIR HANDLER BLOWER DOORS how to find & open the blower compartment door on an air handler or furnace
Or see AIR HANDLER / BLOWER UNITS - home
Or see FURNACE CONTROLS & SWITCHES
Or see HEAT WON'T TURN ON
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