Smoke detector also wired to central air conditioning


Old 06-25-06, 12:08 AM
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Join Date: Jun 2006
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Smoke detector also wired to central air conditioning

Hope someone here can help me. Last night my hard-wired smoke detectors started going off without reason every 5 minutes or so. They are about 15 years old (I know I should have replaced them) so I just decided to replace them, assuming dust build-up and age were the contributing factors.

The first two were a breeze to replace, but the third presented a challenge. The first two had the 3 standard wires, white and black for power and a yellow wire to connect them. The third has five wires, the three standard plus a red and orange wire. Also, when I disconnect the 5 wire detector my central air unit shuts off (i've been told that this is required by NYS code). Same thing happens if the alarm is tripped. My assumption is that these two extra wires are connected to my AC.

My question is: where can I find a smoke detector to replace my old one? I didn't have an opportunity to go to the store today, and so far my online searches have been unsuccesful. Is there any way to use a typical 3 wire detector while bypassing the automatic AC shutoff? As it stands now I have the circuit breaker for the detectors turned off. Unfortunately this also disables power iin my bedroom as well as the outlets in my upstairs hallway, so it is by no means a long-term solution. Thank you to anyone that can help me with my problem.
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Old 06-25-06, 08:43 AM
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Join Date: Jun 2000
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That detector has an additional relay. A number of the major brands like Firex and First Alert make similar detectors, they also make add on relays that operate using the interconnect output of the smoke detector.

The tricky part is finding the parts. They are seldom stocked in home centers.

The setup you have is kinda "old school". The more common tactic now is to install a dedicated duct smoke detector into the HVAC system. These have all of the necessary relays built in, and are powered by the 24v power for the HVAC thermostat control.

You can bypass the HVAC interconnect, the tricky part is not knowing if the output from the smoke is tripping another relay elsewhere, or if the contacts in the smoke detector is being used directly.

A HVAC person can probably find and bypass the interconnect point pretty easily. Right now, there's not enough information to give you a safe answer. What you can do for the short term is disconnect the AC power to the detector (you only need to pull the black wire out of the pigtail and wirenut it off). This will let the wiring harness stay connected without risk of the detector going into alarm while you sort out a correct replacement strategy.

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