Question:
Air cond. triggers smoke detector!I had a split air conditioning system installed. The diffuser is at the top of a wall, pretty close to two smoke detectors (ionization type). The problem is that after using the air conditioning for a few hours, when we turn it off, the smoke detectors set off.

The air conditioning installator never heard of such a situation

Anybody has an idea as to what is happeening?

Answer: I can guess of two scenarios that could be causing a false alarm.

1) You are blowing air and particles into the smoke detector, these particles could be mistaken for smoke.

2) Smoke detectors may be designed for relative humidties into the low 90%'s however by blowing cold air on them it is possible that water is condensing inside the detectors triggering an alarm.

NFPA-72 states that smoke detectors should not be installed within 36 inches of diffusers and grilles. They also list a maximum air velocity probably 300 FPM or somewhere in that range. I guess they do not want the AC blowing smoke away from the detectors.