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jsweney 09-20-2012 07:08 PM

short cycling a/c with honeywell prestige
 
My A/C seems to run very frequently when it's hot (sorry, haven't actually measured it). Is there anything I can tweak on our Honeywell Prestige thermostat to make it cycle less frequently. For example, is there a setting of how much discrepancy there is from the set temp to the measured room temp before it fires the a/c on. As it is now, It always keeps the thermostat measured room temp exactly as currently set, so it must trigger a cooling cycle with less than 1 deg F difference now.

thank you!

Lennox 13 SEER 13axc 3 ton
(supposed to be) well insulated, tight (HERS rating 56, 2.3 ACH at 50 Pascals), new 4000 sq ft home (ranch + basement), 2 zone (basement is still always too cold in the summer, no slab or foundation insulation, air handler in basement)

techpappy 09-20-2012 08:13 PM

should be able to reset the temperature differential of the thermostat to 2 - 3 degrees to make the cycles longer

Also, you should be running the circ fan "continuous low speed " to create constant air circulation..this will help to keep even temps throughout the house and will also help prevent the short cycles,,without continuous fan operation symptoms are 1. freezing basement because cold air is heavier than warm air and is not being properly circulated out of the basement through the house..MUST MAKE SURE YOU HAVE LOW MOUNTED RETURN AIR DUCT IN BASEMENT...2. Erratic temps on main level creating short cycling 3. Too hot on any upper floors or more distant rooms especially on south side or over garage

Your thermostat may already be wired to accommodate this method of operation e.g., Set to "cool on". I believe this may result in the fan running continuously on low speed then kick into a higher speed when TT calls for cooling/compressor starts. If TT isn't set up for this then call tech to rewire to do so.. You will be waaaaay more comfortable and unit should cycle way better.

gregzoll 09-20-2012 09:06 PM

Possibly due to having the house air tight, the hvac may be over sized now. How long have you been there, what kind of thermostat was prev. installed, what is the manufacturer & model# of the inside unit?

jsweney 09-20-2012 10:31 PM

Thank you.

If you know how to change the temp differential, please let me know, I haven't be able to find that setting, thanks!


Yes, I do have the basement zone variable speed fan on continuous and the upper zone on either circulate (30% of the time) or on continuous. It does help, but not completely. A/C is set on upstairs at 77 F and the basement will stay at 68-70, so not freezing, but cool. in the early summer it was about 66 down there and I actually ran the heat in the basement and the a/c upstairs for a short while since we had some guests down there. Very comfortable, perfect temp control, but I realize how bad an idea this is on many levels.

There is a return in the basement, low down, but much smaller than either of the 2 main floor returns. May think about enlarging it, or ducting my ERV stale air exhaust from the basement only (on the main return now). The basement zone supply is perhaps a bit undersized.

Quote:

Originally Posted by techpappy (Post 1014086)
should be able to reset the temperature differential of the thermostat to 2 - 3 degrees to make the cycles longer

Also, you should be running the circ fan "continuous low speed " to create constant air circulation..this will help to keep even temps throughout the house and will also help prevent the short cycles,,without continuous fan operation symptoms are 1. freezing basement because cold air is heavier than warm air and is not being properly circulated out of the basement through the house..MUST MAKE SURE YOU HAVE LOW MOUNTED RETURN AIR DUCT IN BASEMENT...2. Erratic temps on main level creating short cycling 3. Too hot on any upper floors or more distant rooms especially on south side or over garage

Your thermostat may already be wired to accommodate this method of operation e.g., Set to "cool on". I believe this may result in the fan running continuously on low speed then kick into a higher speed when TT calls for cooling/compressor starts. If TT isn't set up for this then call tech to rewire to do so.. You will be waaaaay more comfortable and unit should cycle way better.


jsweney 09-20-2012 11:04 PM

Thank you :yes:
Been there 4 months. It's a LENNOX G61MPV 94.6% 2-Stage / Variable Speed Heating System. Prior was a Honeywell vision pro, which got moved to the basement zone.




Quote:

Originally Posted by gregzoll (Post 1014139)
Possibly due to having the house air tight, the hvac may be over sized now. How long have you been there, what kind of thermostat was prev. installed, what is the manufacturer & model# of the inside unit?


techpappy 09-21-2012 12:18 AM

zoning not working as intended..recommend you find a way to mix upostairs air with basement air to equalize temps..I presume the basement zone control should shut off a supply damper to the basement and similar for main level OR just varies position of single damper in either case cold supply air is still getting into basement areas when not required..does the basement have a temperature sensor/TT that is supposed to control the basement zone ..if so it isn't working ...larger return air in basement mshould improve the situation ..you may also have to increase fan capacity to get better flow of air while in continuous mode

Not sure where you can access differential settings..can you find info on mfg's website or web search? I will also attempt but usually shoiuld be with TT manual

techpappy 09-21-2012 12:44 AM

looked up Honeywell Prestige PDF manual where it shows "basic and advanced temperature control options" and explains you can select "installer settings" where differentials can be set for each stage of heating/cooling So, I assume that means you can scroll through menu(s) until you find "installer settings" and select differential for whichever stage/mode you want..I don't have access to or any experience with these stats but it seems logical to me..hope that helps

jsweney 09-21-2012 11:16 PM

Thank you!

I did find the installer settings, and I found the code. :thumbsup: A bit over my head in there without a manual (or more). I did find a setting for the cooling which allowed me to choose "less aggressive," which may be what I'm looking for. There is also a cycles per hour (cooling or for heat). It was set to 3 CPH after I made this change. Lots of other options. If someone knows if I'm on the right track, or if someone has access to the pro manual, it would be much appreciated, thanks!


Quote:

Originally Posted by techpappy (Post 1014274)
looked up Honeywell Prestige PDF manual where it shows "basic and advanced temperature control options" and explains you can select "installer settings" where differentials can be set for each stage of heating/cooling So, I assume that means you can scroll through menu(s) until you find "installer settings" and select differential for whichever stage/mode you want..I don't have access to or any experience with these stats but it seems logical to me..hope that helps


jsweney 09-21-2012 11:31 PM

Thanks again.... :) The basement zone is closed by its individual supply louver damper when a/c is called for on the main floor upstairs. I vary the var speed fan (always on) from either supplying both the main level + basement, or just the basement alone. Returns always open, and much more flow from the main level returns. I also increased the purge time on the fan to 5 minutes after the end of the cycle, with maintaining the dampers to purge to the zone that called for heat or cooling.

In retrospect, wish I had tried harder to convince my builder to put ~R-5 insulation under the slab, I think it might not be as much of an issue. (couldn't get everything we wanted on the house, $.) I think in the winter it will actually be a bit more uniform temp as both zones will likely be calling for heat. The basement zone has a vision pro thermostat. It has been on continuous fan on w/o heat or cooling for several months now.

Quote:

Originally Posted by techpappy (Post 1014262)
zoning not working as intended..recommend you find a way to mix upostairs air with basement air to equalize temps..I presume the basement zone control should shut off a supply damper to the basement and similar for main level OR just varies position of single damper in either case cold supply air is still getting into basement areas when not required..does the basement have a temperature sensor/TT that is supposed to control the basement zone ..if so it isn't working ...larger return air in basement mshould improve the situation ..you may also have to increase fan capacity to get better flow of air while in continuous mode

Not sure where you can access differential settings..can you find info on mfg's website or web search? I will also attempt but usually shoiuld be with TT manual


beenthere 09-22-2012 08:25 AM

What brand and model zone panel do you have. Do you run your fan 24/7.

jsweney 09-23-2012 05:42 PM

Honeywell TrueZONE HZ322 Panel
Honeywell TTHX9321R5000 Prestige HD thermostat
Yes, fan is on constantly.
Some of the time (15%) I just keep the basement zone open alone on the fan, since flow is very low if both zones open.

Quote:

Originally Posted by beenthere (Post 1015054)
What brand and model zone panel do you have. Do you run your fan 24/7.


beenthere 09-23-2012 08:15 PM

Might want to go to 2 CPH.

If you don't already have one, a dehumidifier for the basement would be a good idea.

Keeping the fan on 24/7 tends to raise the ID humidity.

jsweney 09-23-2012 11:40 PM

Thanks. :)

I'm not sure the Honeywell prestige will go that low CPH. Currently on 5 CPH for heat (which, appart from the above, I haven't really used).

Live in Colorado. Max indoor humidity this summer was 50% and has generally been 35-45%. About 5-10% higher in the basement. Will be turning on my humidifier in the next month.

Quote:

Originally Posted by beenthere (Post 1015994)
Might want to go to 2 CPH.

If you don't already have one, a dehumidifier for the basement would be a good idea.

Keeping the fan on 24/7 tends to raise the ID humidity.


beenthere 09-24-2012 05:14 AM

5 CPH is too hard on an A/C or furnace. Comes out to 6 minutes on and 6 minutes off. On Honeywelll thermostats temp over rides CPH. Most A/Cs don't reach their efficiency rating in 6 minutes of run time. And a furnace barely gets there also.


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