I recently had the following Trane system installed:
XV95 2-stage natural gas furnace (100KBtu)
XL16i 2-stage heat pump (4 ton)
In case it matters: Coil 4TXCD050BC3HCA
Vision Pro IAQ thermostat
My contractor had experience with the IAQ stat, but not with using the DHM terminals to slow the blower in dehumidification. When I asked him about it, however, he was perfectly willing to read through the install instructions and do it that way.
We spent a bit of time scratch our heads over the instructions, though. The installer's guide for the furnace has a section on adding a humidistat. It clearly calls for cutting the on-board R to BK jumper, which he did. The instructions also *seem* to say that you should jumper YLO to O. That didn't make any sense to him, and it doesn't make any sense to me, and he didn't do it. The wording is a bit ambiguous: "On single speed cooling only/ non-heat pump systems, jumper Y to O for proper operation... For two compressor or two speed systems, jumper YLO to O."
I'm wondering if the second sentence should read, "For two compressor NON HEAT PUMP systems ...". Can anyone advise on this?
There also seem to be contradictory instructions regarding the Y1/Y2 wiring for the heat pump. The installer's guide for the furnace shows the Y1 terminal of the tstat wired to the Y1 terminal of the furnace and the Y1 terminal of the heat pump. Similarly, Y2 on tstat goes to Y2 on furnace and Y2 on heat pump. This makes perfect sense to me and is the way he wired it up.
But the installer's guide for the heat pump says to wire Y1 on the tstat to Y2 on the furnace, rather than Y1. It shows Y2 on the tstat wired to BK on the furnace. Oddly, it shows the Y1 terminal of the furnace, with nothing hooked up to it. The instructions also say to cut the R to BK jumper, and add a R to O jumper.
Certainly this method would have the desired effect of slowing the blower to 80% in stage 1 as compared to stage 2. But what's the point of having Y1 and Y2 terminals on the furnace, then? The table of blower speeds in the manual shows different CFMs for stage 1 vs stage 2 in heating mode, but only shows one value for CFM in cooling mode. I assume "heating mode" is aux heat in my setup, and "cooling mode" really means either type of heat pump operation (Y1/Y2 energized). Am I right? Is it the case that Y1 and Y2 on the furnace produce the same fan speed???!!!?
If the wiring needs to be changed to correspond to what's shown in the heat pump manual, it seems I'd have to abandon the idea of using the DHM terminals of the IAQ entirely. Yes?
BTW: One obvious response to my post would be to ask me if I notice a airflow difference between stage1 and stage2 heat pump operation. I'm going to try to answer that question this weekend, BUT.... I'd be shocked if there isn't exactly one right answer to this question, so my observations are really irrelevant.
Any help is appreciated.