ReplyIts the digital programming, and the temp sensor in the unit. typical behavior for them.
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Got a Prestige IAQ in my house. set up for 2 heat/1 cool. Have tried almost every combination possible in the installer set up but whenever I turn the heat up enough to kick in second stage it'll always kick back down to low fire a couple degrees shy of setpoint (like it's supposed to) But then it kicks the furnace off and says "waiting for equipment" and then turns back on about 60 seconds later.
What gives? Previous VP 8320 did this too, not nearly as often as the Prestige though (once in a blue moon). Can't imagine what the thermostat thinks it's doing by short cycling the furnace in the middle of bringing the temp up.
God Speed, Jim. We'll miss you - 2-26-23
Its the digital programming, and the temp sensor in the unit. typical behavior for them.
Global Moderator
Interesting. Didn't think that was typical. Never heard that complaint before as a matter of routine. Wonder if the furnace dropped 24v to the stat briefly. Some brands will do that if the limit opens. Had a VP IAQ owner complain the other day about it and it was the limit opening.
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Odd that the limit would open on low heat but not on high. A way to check to no 24V theory is shut off power to the unit and see if you get the waiting on equipment message.
If you are dealing with a limit switch issue, how big is the equipment in relation to your ductwork? Have you verified blower speed and temp rise?
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That stat can be powered from any 24 volt source, just give it a dedicated transformer then it won't care what the limit does.
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Change the cycles per hour,I don't remember which way. Mine done that when I turned it up very much.
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If it were losing 24v the screen would go out, backup battery only retains the memory in these stats, doesn't power the screen. As for the high limit theory, the temp rise is 38-41 degrees in low and high fire (furnace calls for 30-60)
Wonder if it has something to do with the furnace being oversized, really doesn't even need 2nd stage. 1st can hold 72 at -15 running almost continuous...so maybe the thermostat knows that and thinks it will overshoot or something and kicks the heat off. Got both stages set to 3 CPH.
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72 @ -15f in 1st stage is nuts. What is design temp for your area? How big is that furnace?
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Design temp is around 0. It's an 80k 80%er, puts out 41,000 BTU's in low fire. A/C is sized for a desert too. (part of why I put the Prestige in, trying to fix the installers screw ups)Originally Posted by 54regcab
I wonder if the Honeywell's do this on properly sized two stage systems as well. I remember all the way back to the Chronotherm IV doing weird stuff with cycling off before hitting setpoint too.
God Speed, Jim. We'll miss you - 2-26-23
Once you set it and forget it. It will operate normally. Well, somewhat normally, since you seem to have a grossly oversized furnace.
The IAQ senses both ambient heat, and IR heat.
Professional Member*
Whoa, 41k keeping a house warm down to -15f outside. Is the house small or super insulated? Seeing this makes the whole oversizing thing really hit home... A simple 50k single stage furnace would have done the job...
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Yeah I usually do set it and forget it, but I set it back 2-4 degrees when nobodies gonna be around all day (nice to use my phone to turn it up)
Its the upstairs, which is 1,300 sqft. R30 in the attic R19 walls. Did a cheap load calc almost a decade ago and came out around 30,000 BTUs @ design with 70 in -10 outside and the attic was R19 at that time.
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You can play with the cycle per hour but most likely the thermostat, among other things, is still in the process of learning. I'd go with a reasonable CPH then leave it alone for 4 or 5 days or more until it learns your house.
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Trying it with second stage set to 1 CPH and second stage differential at 1 degree. Tried "Comfort" and it proceeded to turn on and off into second stage only for awhile (skipping over first completely) until it reached actual setpoint. Can avoid the issue by not setting it back and/or locking out 2nd stage but would like it to work right without having to do that.
God Speed, Jim. We'll miss you - 2-26-23
On a grossly over sized furnace, its not gonna work right.
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Yeah pretty much my conclusion, interesting to see how the Prestige tries to compensate for it. Surprisingly the oversized furnace has no freeze/thaw cycles at all. Can't even feel/barely hear it in 1st stage.
Professional Member*
Since you are so oversized have you considered just disconnecting the 2nd stage entirely? Set it up as a single stage.
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Yeah have done that a bit in the past. Always using my system to test out different things so it doesn't usually stay that way. Trying it with a program, and the settings I mentioned above and will leave it alone for a few days see if it "learns"
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Let it go from 66 to 70 on it's own today and it worked how it should, started out in second stage kicked back to 1st then ran a little bit before kicking off at setpoint. Think it has something to do with where I set it, if I go from 66-72 it always short cycles itself but don't notice it when going to 70.
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