For the past few weeks an AHU controller has occasionally - 3 times - seemed to loose it's memory when switching from unocc to occ mode as commanded by the weekly schedule. Although all the points are functioning, valid, and, where applicable, commandable from the front end (Companion), the two points controling the analog outputs to the damper actuator and the heating valve will not sequence in reply to the discharge air setpoint; but will instead remain in their unoccupied state- dampers = 100% closed, valve = 100% open. The space then overheats. I am able to override the points from the front end to whatever value I choose and have visually watch the valve and damper move. The air preasure to the EP4000s is 18 psi with no leaks. Releasing the overrides returns the two points to the unocc default. I have cycled the controller electrically off and then back on and the problem is solved until the next time. Yesterday, after the most recent failure, I redownloaded the config file from HVAC Pro and the controller went to it's proper occupied functioning. I then tried commissioning the controller and when I exited and reset, the two analog points were again not responding. I then cycled the power and all was fine. This morning the points are responding properly. I removed the logic board yesterday to check the various wires, sensors, relays, ect., and all were OK. The AHU was installed and programed five years ago and has given no problems, nor has it been accessed or reconfigured. Because the problem seems to be a failure in occasionally sequencing the AIs from unocc to occ, I would guess that the fault lies in the logic board. Before I purchase a new board, have I missed anything that I should check or troubleshoot further?The controller is AHU 102-0 (REV C06) configured as mixed air single path, supply air reset from zone temp. Thanks for any help or advice.
Mark Schofield, Guildford Board of Ed, Facilities Dept, Guilford, CT