I think the problem is you have the thermostat set at 85 but the room temperature is at 75. The heat pump will not come on since there is no call for cooling. You have a heat pump, not a whole house dehumidifier. The first priority is to maintain the desired temperature. The second priority is to lower the humidity.

You are set up to go up to 3 degrees below the set point in order to reach the set humidity level. Try setting the temperature one degree higher than the room temperature and see if the heat pump comes on. It should come on a run until the humidity level is reached or the room temperature is 3 degrees below the set point. It should stop whenever either is reached.

Thanks Mike. Your were right on the mark. I was trying to use the system as a whole house dehumidifier. And as you suggested, the a/c came on when I set the temp 1 degree above the room temp.

I think I get it now, but I'm unclear about the significance of the 1 degree setting to test the system. Is this is fixed percentage over the room temp or an adjustable parameter?

I'm trying use this setup in our vacation home while we're away. The basement is the high humidity area in the summer while the rest of the house isn't bad. The basement has its own Honeywell thermostat with IAQ features with the dehumidify option. Worst case I'll have to use a basement dehumidifier preferably connected to the thermostat's dehumidifier terminals.

Thanks again.

I suggested setting the thermostat one degree above the room temperature to verify the dehumidify on demand feature is working. If it was not then you would not have seen the cooling system start up. In theory you could have set it up to 3 degrees above the room temperature. Setting no. 383 determines this value.

Don't expect precise humidity control. It is going to vary depending on the conditions.

I once saw a case study of seasonally-occupied homes in FL. IIRC, they recommended dehumidifiers as the primary tool with the cooling system employed to prevent overheating of the homes. You should check me on this because it has been a while since I read it. You might try the Florida land grant university site or the Florida Solar Energy Center.

This is not the case study link, but has some useful advice.

Here is a link that might be useful: This is not the case study link, but has some useful advice.