I've picked numerous of my co workers brain about this, and no one has an answer. Was hoping I could get some insight.
I'll start by saying I have a very basic non communicating carrier 2 stage furnace and 13 seer 1.5 ton Ac. I have a hard start kit on the condensor,not sure this matters.
My problem is that when the temp satisfies on the stat, sometimes the ac will continue to run for another 10, 15,20, even 30+ minutes after temp is reached..no, its not just the indoor fan, and it is not over shooting the temp. If I go 1 degree above, it will turn it off instantly. This only happens in cooling mode, not heating.
I have tried 3 different known working stats. Basic ones, programmable, non programmable, you name it,they all do the same thing. I have 5 wire.
My ac works great, if I drop temp 1 degree below on stat, it'll reach the temp within 10-20 minutes on a 25-30 degree day. It blows ice cold. I have no concerns regarding the operation of the unit from a mechanical standpoint, I'm 99% sure my issue is electrical
Please help, I'm at such a loss, I'll provide any other info needed.
Give us the info on the thermostat, the models of furnace and outdoor unit. Give us pictures of the low voltage wiring at the furnace and the thermostat.
I would say that this issue, isn't an issue at all but in actuality how an anticipated thermostats with a cycle rate algorithm operate. Years ago, when digital thermostats hit the market, specifically Honeywell 8000 series, I noticed the same issue and customer complaints of ac's and or furnaces would run even if the set point was reached. The idea is that if you wanted your house at 21C, why would you want it to rise to 22C before activation.
All thermostats have this CPH cycle per hour settings, Honeywell uses this, white rodgers is a little more confusing with their settings. The thermostat will cycle the ac or furnace 2-3 times per hour (depending on setting) to ensure the set point is unchanged, all the while the thermostat is calculating and averaging pervious run times and room temps. If overshoot occurs, the averaging is recalculated.
when you drop the temperature, or alter the set point to a new one, the thermostat sees the "new set point", activates and runs, but will drive to the new set point and cycle off as it doesn't want to overshoot the set point, essentially it doesn't know how long it needs to run per hour now to maintain room temperature, as you have changed the set point. Cycle rates and algorithms data needs to be recalculated due to the new set point, if you leave it set to the new set point, the cycle rates and averaging will begin again.
In Honeywell thermostat settings there is something called adaptive intelligent recovery, this feature learns how long your thermostat ran today during warm up or cool down program activation. It uses that info to understand how long it needs to run during tomorrow's cycle, so think of it on those terms with respect to the cycle rates.
Quote from: Porcupinepuffer on July 25, 2025, 05:52:54 PMGive us the info on the thermostat, the models of furnace and outdoor unit. Give us pictures of the low voltage wiring at the furnace and the thermostat.
I've tried honeywell T4, t6, and a non programmable Emerson. 2 stage carrier 5 years old, 1.5 ton ac, also 5 years old. 5 wire to R G Y C W, 2 wire to ac, both are non communicating.
Little late here, but if there is an HRV or ERV interlocked with the furnace and is wired wrong this will cause the condenser to run constantly. I'd confirm that the HRV is wired correctly (G from stat intercepted and routed through the HRV relay)