MN- (67538) RM-018-8-u-BA02-349
Noticed the unit having trouble maintaining proper supply air temp(too hot) earlier this spring. Unit had the economizer open 100% yet could not keep up. This system has two sets of dampers, one blade connected to the economizer damper motor and the other four blades(3 in return and one on economizer section)connected to the constant air volume control(VRD-2). Basically the economizer blade was open and the other four blades in closed position. Meaning that the unit was bringing in 50% outdoor air and exhausting nothing. After confirming the wiring was correct and the motor was fine it was determined the VRD-2 control was not operating correctly. Changed with a VRD3 today however the issue remains. That set of dampers basically does nothing 100% of the time, no matter what the economizer is doing. I am able to get the motor to move if I set the VMin to 0% and the VMax to 20-30%, in which case the motor goes full open and after that does nothing. It will only do this if there is no override signal...which makes sense?
The wiring is correct at relay 1(on the closed contacts). The CAVC is getting a 10vdc signal when the economizer is being called for.
I've included the wiring diagram and AAON's Minimum air calibration liturature which explains how the system should operate. What's interesting is that there is no mention of a wire on terminal 4 in the air calibration liturature, yet there is on the wiring diagram and this is how it is factory wired. According to Belimo's wiring diagram this is for a 0-20V phasecut.
I would think that once the CAVC gets the override signal on terminal three that it should allow more fresh air in....or am I way off base?
Another interesting note is that the damper wire was disconnected from the CAVC when I first started looking at this...unsure as to why.
If anyone can explain how this damper system is supposed to operate and if something is actually wrong here I would appreciate it greatly!