Anyone have some experience with these things. My favorite builder is now doing the warranty on the last 120 houses she built and a popular call is "why does my dryer vent fan run all the time"? The HVAC guy who actually installed them is baffled. The EC says he doesn't know much about them but there must be a switch somewhere. Before they start "easter egging" around throwing parts at it I thought I would ask you guys.
I've installed a couple of these things. I think locally, anything over a 8' run (or around there) requires a booster fan. I'm assuming this requirement is to reduce the possibility of a back-up resulting in a lint fire.
They work on a pressure/air-flow switch that senses when the dryer starts pumping out air from the dryer exhaust.
If their fan keeps running, it could be three things: A) the switches are going bad B) the device is installed improperly (backwards - the orientation of the switch & it's little feeder tube in relation to the fan/dryer is important) or C) The GC installed cheapo crap just to knock the job out, and the units are failing for any number of reasons.
I just ran into this on a 159 unit condo complex. There is a kit separate from the fan it is a pressure/air-flow switch (like the one zapped just mentioned) which controls the fan. It has a little vinyl tube that pokes into the exhaust duct and senses when the dryer is running a to turn the booster fan of and on.
This kit is generally furnished and installed by the Mechanical contractor and final 120V terminations are by the EC. Also note there should be an access panel and either a switch or plug for the booster fan for service.
[This message has been edited by ITO (edited 12-08-2006).]
Check to see if the fan actually has a draft sensor. Maybe someone ordered a fan without it and that is why they all run. Otherwise check the vent termination cap. We had some that had to run into a soffitt cap. The townhouses are in a paarticularly windy spot. We finally figured that the wind was actually inducing enough draft to start the motors.