Help with Vision Pro IAQ dehumidification

**alex123** · 08-21-2007, 12:42 PM

Can someone explain how to use dehumidification option on this Tstat.
It is connected to var speed 2 stage HP. Dehum option set to 379-1 dehumidify with AC.Installer Test 6 runs AC @ lowest speed. But if I just lower humidity nothing happens.

**mark beiser** · 08-21-2007, 01:50 PM

What brand/model 2 stage heat pump do you have?

If it is a Trane XL16i, the control can't lower the blower speed to dehumidify because the required terminals in the air handler are already used by the system. The only thing it would do is overcool to dehumidify, and only if the humidity is >5% above setpoint.

**alex123** · 08-21-2007, 04:01 PM

It is York 9V not sure what the number is

**DWB** · 08-21-2007, 08:57 PM

Here's how it's supposed to work. When humidity exceeds the set point, the IAQ trims the blower speed until getting back to the set point. If humidity exceeds the set point by more than 5%, it goes into overcooling until within the 5%.

To function properly, it needs a jumper to DHM1. DHM2 must go to HUM on your ECM control board. Dip switches must be set properly and the HUM jumper must be clipped (PJ6 on mine).

I don't know what to tell you about test mode. I don't bother with it. If the function works, it works.

**alex123** · 08-22-2007, 08:07 PM

So t-stat does not turn Ac on on humidity alone? Only overcools when there is call for AC? Is this correct?

**DWB** · 08-22-2007, 08:17 PM

Correct, the stat doesn't activate anything on humidity alone. It only overcools when RH goes more than 5% above the set point.

**mayguy** · 08-22-2007, 10:25 PM

The t-stat will slow down the blower if it's wired right on call of cool..

If the humidity goes over 5% of set point, then it will "over cool" up to 3˚ below set point.