Carrier Mixed Air Damper Algorithm

[red warrior]

I'm having trouble setting up a mixed air damper algorithm in Universal and Comfort Controllers. I can make it hold a mixed air temp in the air handler when the outside ambient is cold. On dual duct set ups I try to hold mixed air to 55 deg. I set up the master loop to modulate return and outside air. This gives me cooling when mechanical cooling is locked out. But when the outside temps warm up above 55 and I can't maintain this temp, I want the dampers to shut down and draw return air while compressors are needed. The way it is now when outside temps are to warm the outside air damper just opens to 100% open and sucks warm humid air into the air handler. What am I missing?

[Balibe]

Do you have a NTFC setup and linked in the MADVV?

The NFTC does the outdoor air calculations for the MADVV so it knows if OA is good for cooling. If you have both OAT & OARH, you can calculate on enthalpy instead of just OAT. It can even work better if you have RAT & RARH.

[okfrommyhouse]

I've always thought the MADVV was kinda tricky. Like Balibe noted, you have to set up the Night Time Free Cooling so it knows the outside air conditions. It is trying to maintain a mixed, or (supply air temp) 3dF below the calculated setpoint in the linked CCV algo, so you really need to have some type of supply air reset going on.

To troubleshoot it - I would force the the compressors off and play with forcing the outside air & space sensor inputs. Watch the calculated setpoint in both algorithms maintenance tables and that should provide a clue as to what is going on.