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I have two Honeywell T8602D thermostats running thru a MABS2 zone panel to control a Trane XV90 60k/85k (I think) BTU forced-air furnace. There are two AOBDs for zone 1 and one AOBD for zone 2.

1. On the T8602D thermostat, Option 4 lets you set the number of "Heat Cycles" per hour. The contractor left it on the default of 6 for "Standard Efficiency" and I changed it to 3 for "High Efficiency" since that's what I have. The old furnace just ran until it reached the set point. What is the theory and actual practice behind this cycling?

2. There is no "isolation collar" between the furnace and the ductwork. This is a black canvas-looking fitting that separates the sheet metal from the furnace. The old furnace had one and in a past house the Lennox High Eff. furnace had one. The contractor said they don't use them because these Trane units are so low vibration with the DC motor yadda yadda yadda. But I complained repeatedly about the vibration telegraphing thru the ductwork and structure. For example I showed them stuff vibrating on the dining room table right above the furnace. They changed some mounting brackets so they were more secure but the problem is not solved. The problems mostly occur when the inducer starts up but also on Stage 2 to a lesser degree. Any pro opinions on this?

Background:
[Begin Rant]
Lots of stuff was set up incorrectly or screwed up by the first three installers that the contractor sent (Got to the point where I had to make sure my wife wasn't around when they were here). According to the contractor, two of them had to be "let go" for reasons unrelated to our job and the third quit on his own. And I had hired this outfit on a relative's glowing recommendation!

The fourth guy finally straightened out a bunch of things, and I will give the contractor credit for eventually delivering, but the relationship has been, shall we say, damaged. Their first mistake (after bidding on the job!) was telling me it would take a week, and this was after my detailed RFP, proposal from them, very limited price haggling, and a site visit by an "experienced" tech. They started in mid-July. About a month later the A/C was working. They got the heat running in mid-September, and finally got things working smoothly in the first week of February. I've had lots of contractors in my house, some of whom I just picked out of the yellow pages, and the HVAC folks were the worst communicators, biggest YES men, and worst at follow-up. OK, I feel better now.
[End Rant]
 

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Not a pro opinion.
I replaced one A/C last August (Trane XR12) and it was a difficult air handler in the attic install. The contractor that I chose was flawless. Showed up on time, completed on time, cleaned up pretty well for a crew that had just spent a day in August in a FL attic (it must have been 130 in there).
Maybe you should have done a little more homework when deciding on a contractor.
 

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Discussion Starter #3
Teetorbilt said:
Not a pro opinion.

Maybe you should have done a little more homework when deciding on a contractor.
Agreed. I figured checking BBB and two references on similar jobs was enough but that didn't do it.

Again, to be fair, the contractor has fixed everything on the three-page punch list except this vibration issue. These were things like, Humidifier is not working ... Install ductwork to cold air return in dining room ... Damper to north side of first floor is stuck closed ... Stage 2 never runs ... Light showing around A/C lines thru side of house ...

I learned a lot in this process but my wife will be reminding me of this for years to come.
 

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You really need to get the vibration issue addressed, over time it could cause major problems. I think that you have given this guy enough chances and I'd call Trane direct.
Why did God give women those memories? Mine loses her car keys at least once a day but can vividly recall a minor mistake made a decade ago or, in the case of her brother, 40 yrs. ago.
 

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xv90 furnaces are generally very quiet
if you can see things vibrate on the table something must be out of balance
is it an attic, crawlspace or basement install?
 

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Discussion Starter #6
Comfortman said:
xv90 furnaces are generally very quiet
if you can see things vibrate on the table something must be out of balance
is it an attic, crawlspace or basement install?
Basement. It's sitting on firebricks on the concrete floor.

This is a GE inducer, CCW, 5200 RPM. I checked the rubber isolators on the motor mounts and they seem fine, with a reasonable amount of play.

The only preventive maintenance listed is to vacuum the exposed vanes. At least in the book I have. It's been running this way for four years, so if something has been wrong with the furnace all this time, it's a pretty slow burn.
 

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okay several things
the canvas connectors in the ductwork would help reduces duct transmission
(noise carried by duct)
the vent pipes should not be strapped tightly to floor joists but loosely hung
the vent pipes should not be in firm contact with the duct or anything else they could transmit vibration to
the motor should not have to turn anywhere near its full rpm to make that pressure switch(in fact it monitors switch closing to maintain the MINIMUM rpm possible)
if there are reducers in the vent run OR if the venting sags anywhere OR the vent run is very long and wasnt bumped up one size then the motor will have to turn very fast to close the switch
if none of those factors are present i would try a new inducer assemly, its possible the wheel or shaft is bent
you (by that i mean I) lol can easily look at a wheel and tell its out of balance
you spin it and it either spins true or it wobbles
hopefully your service tech actually removed the inducer and visually inspected the wheel
those inducers should be very quiet relative to fixed speed units

as to air noise alot of that has to do with duct design and sizing

hope this helps

scott
 

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Discussion Starter #8
Comfortman said:
okay several things
the vent pipes should not be in firm contact with the duct or anything else they could transmit vibration to
Good call. In fact I noticed that the combustion intake and exhaust pipes are laying unsupported on top of a return air duct!
Comfortman said:
the motor should not have to turn anywhere near its full rpm to make that pressure switch(in fact it monitors switch closing to maintain the MINIMUM rpm possible)
if there are reducers in the vent run OR if the venting sags anywhere OR the vent run is very long and wasnt bumped up one size then the motor will have to turn very fast to close the switch
What or where is the pressure switch to which you are referring? The vent run is about 20' and it is 3" PVC to the sidewall Bayvent which does NOT ice up. I can hear the inducer spin up high for a few seconds when the furnace starts and when it goes into Stage 2, but then it drops.
Comfortman said:
its possible the wheel or shaft is bent
you (by that i mean I) lol can easily look at a wheel and tell its out of balance
you spin it and it either spins true or it wobbles
Oh man! I spun it by hand and it feels like it's weighted on one side. That is, it only goes a revolution or two, then it just stops with a jerk. Is that what you mean by wobble? I thought maybe that had something to do with this being an ECM but I guess that's wishful thinking. This sounds expensive. But what would have caused this? If it's already shot can I just run it into the ground?
 
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