Honeywell IAQ Dehumidify Question

[Todd546]

I have read various posts of people with similar problems but I cannot get my IAQ to succsessfully use my A/C to dehumidify. I have ...

Furnace: Carrier 58PAV135-20 series 151 (single stage)
A/C: Carrier 38CKB060300 (single stage)
Humid: April Aire 600 [currently not connected in order to simplify setup pending resolution of dehumid problem]

First off, I have no experience wiring this level of complexity tstat, but with such a basic setup, I figured there would be little problem.


My IAQ is set to fan(auto) and system(auto) with dehumid set to 45%. The heat temp is set to 65 and cool to 77. The current indoor humidity has been between 60-70% all day and the A/C will kick in reducing the indoor temp to 3 degrees below the cool setpoint (as per setup function 0383 I assume) but will not continue cooling to reduce the humidity.

What strikes me as odd is that on the dehumid screen, the AUTO/OFF option is present ... even though setup function 0379 (dehumid control) is set to 1 (dehumid with AC). The Operating Manual (p18) specifically indicates that AUTO/OFF option is only present when using a whole house dehumid and is not present when dehumidifying with the AC.

For clarity, I have the AC wired to Com and Y only, not DHM.

Any and all help is greatly appreciated.
Todd

[t527ed]

diy not allowed here.......

[beenthere]

You need some modifications to your unit.
The IAQ will run your system to cool, but since you don't have a VS blower for it to slow down, it won't be able to actually dehimidify.

Any competent contractor, can easily make teh alterations for you.

[Todd546]

Allow me to clarify DIY-"appearing" thread:

I just bought this house about two months ago. The sellers provided proof of "maintenance check" of HVAC system as condition of sale. Now that the deal is done, I have noticed the peculiarity described. I have contacted the company that performed the maintenance check and they will come out to check my concerns ... for $75. Before I invest this money, I want to know if I have a legit concern or if a simple incorrect setting was originally missed.

[nvr2old]

A maintaince check to the person selling the home my only mean change the filter, clean the condenser, blow out the drain, and verify there is some refrigerant in the system, I do not want to spend anymore money on this house I'm selling it. A maintaince check is usually interpreted by the home buyer to mean the a/c is correctly sized for the house, everything is running like a fine swiss watch and my utility bills will very low.

[teddy bear]

I have read various posts of people with similar problems but I cannot get my IAQ to succsessfully use my A/C to dehumidify. I have ...

Furnace: Carrier 58PAV135-20 series 151 (single stage)
A/C: Carrier 38CKB060300 (single stage)
Humid: April Aire 600 [currently not connected in order to simplify setup pending resolution of dehumid problem]

First off, I have no experience wiring this level of complexity tstat, but with such a basic setup, I figured there would be little problem.


My IAQ is set to fan(auto) and system(auto) with dehumid set to 45%. The heat temp is set to 65 and cool to 77. The current indoor humidity has been between 60-70% all day and the A/C will kick in reducing the indoor temp to 3 degrees below the cool setpoint (as per setup function 0383 I assume) but will not continue cooling to reduce the humidity.

What strikes me as odd is that on the dehumid screen, the AUTO/OFF option is present ... even though setup function 0379 (dehumid control) is set to 1 (dehumid with AC). The Operating Manual (p18) specifically indicates that AUTO/OFF option is only present when using a whole house dehumid and is not present when dehumidifying with the AC.

For clarity, I have the AC wired to Com and Y only, not DHM.

Any and all help is greatly appreciated.
Todd

Without getting into the detail of equipment, here are a couple suggestions. Over cooling 3^F is the t-stats simple way of dehumidifing. The basics of maxing the moisture removal of the a/c is slow the air flow over the cooling coil to all the coil to get cold enough. Coil temps of 45-50 remove more moisture. The limitations are coil freeze-up and sweating ducts. Typically, you need enough cooling load to remove 5-8 gals. of moisture per day to maintain <50%RH. A 3 ton a/c removes a gallon of moisture per hour. 5-8 hours of cooling is needed at a minimum to maintain <50%RH. Cooling to 78^F with a 3^F over-cool for dehumidification will not get you to <50%RH during wet cool weather.
Using a whole house dehumidifier like the Ultra-Aire will get you <50%RH during low/no cooling load conditions. These units are added to your a/c. The dehu with a well tuned a/c will provide any temp/%rh combination you want. Check my posts for more discussion. Regard TB
PS I use a system similar to yours and have posted data.

[mayguy]

Why do you have the IAQ on a very basic single stage non-variable speed furnace.

[beenthere]

Maybe he plans to get a VS furnace later.
And doesn't want to pay for a stat twice?

[Airmechanical]

Why do you have the IAQ on a very basic single stage non-variable speed furnace.

even with a multi-speed non variable speed furnace;

a standard relay can be used in conjunction with the IAQ to lower the fan speed on a call for dehumidification!



.

[mayguy]

even with a multi-speed non variable speed furnace;

a standard relay can be used in conjunction with the IAQ to lower the fan speed on a call for dehumidification!

True, and hope the coil has a TXV on it.

[badtlc]

What role does the TXV play in this? What about the TXV helps dehum?

[t527ed]

What role does the TXV play in this? What about the TXV helps dehum?

txv will help prevent turning the evap coil into a block of ice if you slow down the indoor blower to dehumidify.

[badtlc]

txv will help prevent turning the evap coil into a block of ice if you slow down the indoor blower to dehumidify.

I assumed that from his response. I'm asking how the TXV physically does it. What properties of the TXV provide that assistance?