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?

[mayguy]

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

I take it your not an HVAC Tech?

TXV has a bulb that will sense the suction line temp (super heat) and control the amount of liquid going into the coil.

[beenthere]

TXV won't really prevent the coil from freezing.

It will however slow it from happening. And help to prevent liquid flood back to the compressor. By controling liquid flow to the evap.

[badtlc]

That is what I was wondering. Thanks.