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new system, now more humid than before

6K views 50 replies 10 participants last post by  Dale Gribble 
#1 ·
I had my HVAC system changed out a month ago and now it's uncomfortably humid and muggy inside my house that I need to run the AC 4°F cooler and the fan set to ON just to be comfortable - so much for energy savings.

My house is 1107sqft. Previously I had a 2 ton unit. The old unit cooled, but would run for 14 hours on a hot day and our electric bill was sky high. In addition, the lights in the house would dim every time the compressor would cycle. Fearing that the old unit would decide to stop working in July or August we got it replaced in April.

Previously I have had more insulation blown into the attic, minimum R-38 and installed an attic vent as we only had soffits before.

In the beginning of April I had a new single stage 2 ton outdoor unit installed, a new gas furnace with variable speed blower, and new evaporator coils (of course). I got a fancy Honeywell Vision PRO 8000 thermostat that is supposed to monitor and control indoor humidity.

Since I had this new system my house has been more humid than ever. RH is constantly above 60%, and ranges from 58%-66%. Yesterday's RH outside was 40%. Once the sun went down it was nicer outside than inside.

The new system cycles much more than the old system. I don't see any error codes indicating a short cycle (but that doesn't mean I'm not missing them). The system will run for a few minutes and then supposedly the fan will slow down to continue to cool the house, up to 3° cooler than the thermostat is set to in order to draw out excess moisture. It is not working as it seems it should. Basically, I could have kept my old system, turned the thermostat to 73° and bought a dozen humidifiers and I'd be in the same place and could have bought a boat instead.

Does anyone have any insight on what the problem might be? Could damaged evaporator coils be causing this?
 
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#32 ·
That model Th8321 can slow the blower on a dehum call. It has the U terminal. Its a "Universal" terminal. Can be ued as a normally opened, or normally closed switch.
 
#39 ·
I checked out the installation manual and current wiring. In order to properly utilize the variable speed blower there needs to be a jumper between R and U/1, and U/1 needs to be connected to the furnace. Correct? Do I still need to use C with this wiring configuration?

Can the variable speed blower be controlled with the current wiring with the Honeywell IAQ thermostat or are additional wires still needed?

Tonight I'm going to check the thermostat's set up configuration. I'd bet almost anything the factory default settings haven't been changed and its programmed for single stage heat and single stage cool.

I just want to be 100% before I bring this up.
 
#40 ·
Don't jump R to u1. You would use the U1/U1 to break your com to dehum in the furnace.

Of course, you need the wires ran to the thermostat to be able to do it.
 
#45 ·
Sometimes its a case of the salesman promising the world. And the actual installing crew delivering only what they know.

Sometimes, its a case of, they saved a couple bucks by using the cheaper thermostat, and not running the extra wires it would have needed. And unfortunately, a lot of costumes gt taken across on this.
 
#46 ·
Unfortunately for the installer it was the service manager who sold me the system and the same guy installed this thermostat after the fact as the techs who did the change out had initially installed a VT3000 TALKING THERMOSTAT.

Right Away I told them this isn't what I bought and they said it was a miscommunication at the office. I guess when he showed up to put the right one in he either didn't have the balls to admit they needed to get a different thermostat or they intentionally brought the wrong thermostat to save a few bucks.

I'll have the IAQ by the end of the week.
 
#47 ·
What effect did the additional insulation have on the old unit....or wasn't it done until the new unit? The crawlspace needs to be ventilated. Pick up a cheap hygrometer (spelling) and check the attic, the crawl space and place it over one of the vents when it's cooling. It's very possible that your old unit was performing weekly which effectively could make it equivalent to a 1 ton unit....it ran longer and therefore took more humidity out of the structure. What was the supply temperature at the vents with the old unit?...and now the new unit? What calculations were done to show you actually needed a 2 ton unit, especially after your R-38 attic redo?
I have a 3 ton unit for 2800 sq ft.
 
#48 · (Edited)
I know it's been a couple months but I thought I'd give an update. Well, within a week of my last post I had the tech come out and "fix" it again. This time he put in a Honeywell IAQ with the control module and was able to utilize 3 of the four wires already installed.

He also adjusted the CFMs from 1,200 to 800 (2 ton) . He told me he thought he had done that already, but there are two CFM settings on the furnace: AC and Circulate. He had previously only adjusted the circulate CFMs to match my tonnage.
After the new thermostat and the CFM adjustment I noticed an immediate increase in my comfort. However, the next day I noticed that once the temp reached the target point the outdoor unit would shut off while the indoor unit would continue to run in attempt to bring down the RH.

The next day the outdoor unit would not kick on and the indoor unit would not shut off.

Tech came out and checked the unit. The common wire had come undone at the connection on the board in the furnace. He also said he had the IAQ set to dehumidify with a whole house dehumidifier and not by AC.

Tech said problems were fixed and he left. I took a look at the IAQ and he had just set it to dehumidify off. Idiot.

I set it to dehumidify by AC and now it works like a charm. It's been almost 2 months now. It is continually 73° and 40-45% RH. I live in Tallahassee, which might be one of the muggiest cities (big town really) in the country. For the month of May I used 33% less kwh than May 2011 (1090kwh vs. 1640kwh). Which is about a $70 savings for me, which I'm pretty satisfied with when I can keep it that cool, which I've only ever been able to do in January.
 
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