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greenjp 07-10-2012 07:54 AM

Trane XV80 & Honeywell IAQ setup
Had our system replaced last week with a 3.5 ton XR13 AC, 80k XV80 furnace, and Honeywell IAQ stat. I was reading the various manuals and looking at the settings (I am a nerd mechanical engineer and like to know how things work) and found a few things that seemed off, wanted to get some insight before the tech comes back later this week for a checkup (the furnace makes a rattling/clunking noise at fan start up). System maintained temp at 75 deg and humidity ~50% during our ridiculous heat of the past few days FWIW.

Dip switches S4-1 and 2 are both set to On and it seems the ComfortR profile is active whenever a cooling call is made.

The IAQ is set up for dehumidify with AC (379=1). The system definitely turns on the AC if the measured humidity goes 5% higher than the setting. Overcooling limit is set to 3 deg (383=3) and this seems to work correctly too. What is not clear is if the wiring is set up correctly to run the blower at the reduced speed for dehumidification. Here's what I see inside the EIM:
From IAQ:
1 - red
2 - white
3 - blue
From EIM:
C - white to compressor, blue to furnace
R (hard jumpered to RC and RH) - red to furnace
W1 - white to furnace
W2 - black to furnace
Y - red to compressor, yellow to furnace
G - green to furnace
All other terminals are unused. At the furnace I see the following:
Y - yellow
W - white
W2 - black
R - red
G - green
C - blue

Neither O or BK are connected, nor are there any jumpers. Based on my research here and elsehwere there should probably be some additional wiring. Per the IAQ manual, in the EIM it seems that R should be jumped to DHM1, which should then be wired to BK in the furnance (also see references in other docs to jumpering R and BK in the furnace which I believe would net the same result). Then per the furnace install guide note 10, "A jumper must be placed between 'R' & 'O' to enable the 'BK' circuit or enhanced mode (ComfortR). This 'R' to 'O' jumper must be in place for humidistat dehumidification and proper blower operation with a two step scroll compressor." Don't have a two step compressor but the note about ComfortR is confusing because it seems to be working without this one. Then per the ComfortR pocket guide (note 2 under "Air Conditioner with Gas Furnace") there should be a jumper between Y and O. Apparently different instructions have me confused

Additionally, some of the dip switches are confusing. Note 9 in the furnace install guide states "...S5-2 switch must be set in the 'Off' position if humidistat is used. The 'S5-2' switch must also be turned to 'Off' when applying an airflow command signal to 'BK'." The S5-2 switch is actually set to On. I guess since the wiring described above isn't there this is "correct" for the time being?

Last, for 2 stage heating - the wiring looks correct per the manuals (EIM W1 and W2 wired to furnace W and W2). Dip switches S7-4 are all Off, so I think that means no 2nd stage heat delay (correct for stat control of this feature?) and the default 90 second heat off delay. But then in the stat, it appears to be set for 1 stage heating - 176=1 and option 250 (CPH for 2nd stage heat) does not appear.

So, it appears that both the dehumidification and 2-stage heating features are setup sorta half correctly, and that while ComfortR is definitely working I saw a few references to jumpers that should be in place that aren't. Any thoughts would be greatly appreciated, want to make sure this thing is set up correctly.


hvactech126 07-10-2012 06:12 PM

...You are correct.
Jumper R to Dhum1
Dhum2 to BK on furnace PCB
Jumper Y to O on furnace PCB
You may have to Cut R to BK jumper on furnace PCB - small wire sticking out of control board above low voltage terminal strip on PCB.... with a full model number of your furnace I can verify about this jumper or a dip switch setting.

greenjp 07-10-2012 06:32 PM

Great, thanks a lot. I did not see the R to BK jumper on the furnace board (is this the one referred to as the 'W14' sometimes?) so the installers may have removed it already. My furnace model # is TUD2C080B9V4VBA.


hvactech126 07-10-2012 06:48 PM

Your furnace uses a dip switch and requires it to be in the off position.

greenjp 07-10-2012 07:05 PM

Ok, so in addition to the jumpers and connections above, the S5-2 dip stick needs to be set to Off? Can you comment on how this setup interacts with the ComfortR profile? Does it apply additional speed reduction, extend the 80% operation time, override it entirely? Thanks!


hvactech126 07-10-2012 07:14 PM

it should override it.

greenjp 07-16-2012 03:03 PM

Here's an update:
The tech who came by to check out the "rumbling" upon fan motor start (he did something that alleviated that) was not familiar with wiring the IAQ and XV80 for DOD. He seemed to know all about how to set it all up if there's a 2 stage compressor but doing it with a single stage was new to him. So we got it wired up per the discussion above (RH to DHM1 on the EIM, DHM2 to BK, dip S5-2 to off, the aforementioned R to O jumper already in place - I'd missed it somehow during my initial inspection) and it does seem to be working now.

I fooled around with the humidity set point while the system's been running and it clearly slows down the fan if the setting is below the actual. Once you put the setting above the actual, it speeds right up. It won't turn on the AC independent of a cooling requirement unless the set point is over 5% greater than the actual, which is how it was behaving before.

I still have ComfortR enabled. I like the ramp up and down, as it makes the system coming on and off less noticeable. We also have a 4 ton coil with our 3.5 ton compressor, and our area tends to be humid so I figure the additional CFM reduction over that first 8.5 minutes can only serve to help. Possibly some efficiency loss but I'm assuming it'd be pretty marginal and we don't spend a ton each year on AC bills anyway. The install guide for the furnace indicates about 1350 CFM in the 3.5 ton/normal configuation, so two 20% reductions from that gets it down to ~865 cfm. Assume it's safe to operate in this manner? Thanks,


scottmcd9999 07-16-2012 03:07 PM

Low CFM can cause freezeups, but if you're only doing this during the initial ramp up/down, and during the dehumidification cycle, then you should be okay.

greenjp 07-16-2012 03:12 PM

I believe it's running at ~540 cfm for the first minute, then ~865 for the next 7.5 minutes, then up to 1080 for the remainder of the cooling call if the dehumidification command is active. If the furnace was set up for the nominal 350 cfm/ton (vs the 400 I have it at now) with no dehumidifcation slow down it would run at ~1160, so I'm going on the assumption that 1080 isn't too low.


beenthere 07-16-2012 06:44 PM

Comfort r is useless when you have the IAQ controlling the blower for humidity control. it also waste electric when your outdoor temp is near design and the A/C is cycling on and off. It still slows the blower even though the humidity is below set point.

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