Very short run cycle from a VisionPro thermostat?

[bobk4000]

Has anyone encountered a very short (5-10 seconds) start and stop cycle with the Honeywell TH8320 VisionPro thermostat when it changes from one schedule to another? A couple of days ago my A/C started up and ran for maybe 10 seconds when the thermostat changed from the "Wake" schedule/setting to "Leave", where the set temperature went up by a couple of degrees.

Here’s my setup for cooling: 6AM – 74 degrees (Wake), 8AM – 76 degrees (Leave)

At 7:59 AM the indoor temp showed 74, with the "Set to" indicating 74 as well. The thermostat clicked and the A/C started up. Not 10 seconds later, the clock on the 'stat switched to 8:00 AM, and the "Set to" now displayed 76, and the thermostat clicked off the A/C.

I dropped a line to Honeywell asking for their thoughts, and I was told to check the cycle rate. The thermostat is set to 3cph, the default, and I’m running a single stage A/C and furnace. To be honest, I don’t think I got my point across to the folks at Honeywell describing my issue, based on the response I received.

I’ve only had the short cycle happen once with the A/C, and I did have it occur a couple of times with the furnace starting up, running for maybe 20 seconds, and shutting down due to a schedule change. It’s more of random chance where there is a call for cooling (or heating) right at the time of the schedule change, but I don’t think it is right. My last thermostat, a real oddball Johnson Controls programmable would run one cycle if it started right before the schedule change.

Thanks in advance,
Bob

[travisfl]

Originally posted by bobk4000
At 7:59 AM the indoor temp showed 74, with the "Set to" indicating 74 as well. The thermostat clicked and the A/C started up. Not 10 seconds later, the clock on the 'stat switched to 8:00 AM, and the "Set to" now displayed 76, and the thermostat clicked off the A/C.

Sounds like normal operation to me. The 'stat called for cooling but then the program changed to a higher temperature, so that 'stat quit calling. One could argue that Honeywell should "look ahead" with their programming and not call for cooling within (some time period) but then someone would complain that the thermostat isn't working properly in THAT situation. Running for one cycle would cause the temperature to ramp up/down above/below than the setpoint.

[mayguy]

Sounds like it's working like it should..

Mine does that once in a great while. I just leave mine alone for A/C, but use the program for heating.

THere is no harm done on that. The other t-stats I had in the past done the same, and never made a concern about it.

[tpa-fl]

I've never noticed that with my stat, but I can see how it could occur. Do you have adaptive recovery enabled on the stat? Even if it does only do a 10-20 second run, that cycle start probably is part of the cycle per hour equation. I know the stat disregards cph on the first cycle when you manually change the setpoint and starts the next cycle immediately if needed, barring any compressor lockout delays. If it does happen, it should happen rather infrequently, enough so that it won't adversely affect the life of the AC system. The mercury in the old mercury stats rapidly bouncing back & forth & rapidly cycling the equipment when the stat is being adjusted is far more harmful.

[Edited by tpa-fl on 06-29-2005 at 02:50 AM]

[bobk4000]

I do have the adaptive recovery enabled on the thermostat - and that seems to be working well. In fact, I like how well it hits the desired temperature when I wake up on winter mornings.

With all the smarts built into the thermostat, I "assumed" that it would anticipate upcoming changes in the schedule, and either not call for cooling, or run for a minimum amount of time. My last thermostat did have that feature, along with a lot of other quirky behaviors.

Thanks for insight and answers.
Regards,
Bob.

[docholiday]

That sounds like a cooincidence and no big deal.

When it sets back (to a higher cooling temp), the adaptive recover has no function. However, when lowering the cooling temp, thats when it comes into play in order to have it at set point at the desired time. Visa versa for heating. When raising the temperature it uses the function, when lowering or setting back it does not.