Dehumidfy function works backwards.....

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Old 06-16-12, 07:36 AM
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Dehumidfy function works backwards.....

...No, it doesn't add add humidity when in dehumidify and visa-versa. This spring I DYI'd a complete Goodman HVAC system. MVC950905DX furnace + AC. (Yes, I had a pro check everything -and charge the AC- before firing her up the first time). Everything works perfectly EXCEPT -there would have to an "except" or I wouldn't be here right? I have a Honeywell TruIAQ humidistat connected for humidify and dehumidify functions. My understanding is that when running the AC when the humidistat calls for "dehumidify" it should slow the air handler down to about 85% of normal CFMs. Well it speeds it up instead. Here's how it is wired. On the humistat I have a jumper from "R" to "DEHUM 1" for 24V and I have "DEHUM 2" connected to the "DEHUM" terminal on the furnace. When the AC is running with no call for dehumidify, it runs at 1200CFM (3ton unit), when I set the humistat to call for dehumidify it "increases" to 1400CFM instead of dropping to 1050CFM like I would expect. I thank you in advance for any help you might give.
 
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Old 06-16-12, 07:50 AM
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Which thermostat are you using to control the furnace? Which a/c are you using? 2 stage a/c? Do you have the jumper installed between Y1 and O on the furnace LVTB? Did you turn the DEHUM dip switch to ON?
 
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Old 06-16-12, 09:01 AM
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Honeywell

FocusPRO TH6000 Thermostat. The compressor is a Goodman single stage GSX13036. I have jumpers installed on the furnace TB between Y1 and Y2, and between Y1 and O. It is set for profile "B" and that does work correctly. Yes the DHUM dip switch (S5 #9) is set to ON.

Thanks!
 
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Old 06-16-12, 09:05 AM
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Make sure the trueiaq is setup to open the circuit between R and DEHUM upon a call for dehumidification.
 
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Old 06-16-12, 09:13 AM
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That makes sense....

...could you explain how. I looked in the advanced set up functions but really didnt see anythnig that addresses opening that curcuit verses closing it -like I think it is currently doing.

Thanks.
 
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Old 06-16-12, 09:33 AM
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I'm on my mobile so I can't access the instructions at this time... please pm jay11j for further help today. I'm off to the lake!
 
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Old 06-16-12, 09:46 AM
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The setting is #45, set to 0.
 
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Old 06-16-12, 09:47 AM
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Thanks

for your help and have fun at the lake. I'll PM j11j
 
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Old 06-16-12, 09:54 AM
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Wow

you guys are good! Thanks so much for your help! I won't be able to test it for awhile, but I think you've found the solution. I salute you my friends!
 
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Old 06-16-12, 09:56 AM
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Let us know when you do use it.
 
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Old 06-16-12, 10:20 AM
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Well....

when I set function 45 to 0 I get no dehumidify function. Or more accurately, it stays in DEHUM mode. it runs a 1200CFM and htere is no way for me to raise the humidity the H/S is calling for to see if the AH speeds up. If it did, I could just lower the overall speed to make it 1200CFM and then if the HS calls for a reduction it would slow to something lower.
 
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Old 06-16-12, 10:32 AM
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Now I see

that function 50 will allow me set the upper DEHUM limit to as high as 80%. this will allow me to set the HS above ambient so I can see if functions correctly. i'll ge back later -probably tomorrow- but that for the direction.
 
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Old 06-17-12, 08:36 AM
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Starting to figure this out

I see now that by applying or removing 24V to the DEHUM term of the furnace it increases or decreases the CFM by aprox 20%. Now I just need to figure out how to make the TrueIAQ accomplish that. Right now the circuit of the TIAQ that controls that voltage is N/O and when there is a call for dehumidify it closes and applies 24V to the circuit, raising the CFM which is the opposite of what I need it to do. When I set function 45 of the TIAQ to 0 I get no dehumidify function at all. The DEHUM control curcuit is N/O and stays there. So I need to find a way make the TIAQ DEHUM circuit N/C and when dehumidify is called for to open, removing the voltage and reducing the CFM. I think it might be possible to make the TIAQ work that way by utilizing the advanced set up function, but I'm not sure. Thanks.
 
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Old 06-17-12, 08:41 AM
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Yes. You are correct it should be a normally closed circuit and open with a call for dehumidification.
 
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Old 06-17-12, 08:58 AM
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Thanks, do you know if that can be accomplished utilizing the setup functions of the TIAQ or am I going to need to wire in a relay? Thanks
 

Last edited by GPD3DYI; 06-17-12 at 10:24 AM.
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