Short cycles bad for compressors?

13 years ago

I've read so much about short cycles being bad for compressors but what can you do about it? It seems normal that if you set your t-stat at 76 and it takes 8 minutes to bring it to 76 and 10 minutes for it to rise again to that temp. and again turn on heat pump. During the day my heat pump(San Antonio, tx-HOT)will cycle on for about 12 minutes and off for about 7-10 minutes until approx. 10 pm when it will cycle on for about 7 minutes and off for up to 45 minutes(or longer overnight). Isn't it just doing it's job regardless of the short cycles? Thanks for any input. Tedrik

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Comments (8)

neohioheatpump
13 years ago
If you have a nice thermostat you can control the cycle times per hour. Lower is better.

I have mine setup for the minimum amount of cycles per hour which is 1.

So Instead of running 10 minutes then being off 10 minutes, it will run for 1/2 hour and then it will be off for 30 minutes.

The temperature fluctuates more but that is ok. Its better for the equipment and probably more efficient.
tedrik
Original Author
13 years ago
Thanks-I do have a programmable thermostat, however I can only program the days of the week broken down into temp. for morning-day-evening-night and start time for each. Way too complicated IMO-ex. the default(if programming) is 78 degrees morning, 85 day, 78 evening, 82 night. I can alter these temps and start times but it would be a "crapshoot" to determine the cycle times. Wish I had your t-stat where I could enter the temp and separately enter the length of compressor run time.
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I hadn't give thought that you might think I was infering dishonest about cleanleness until A Air commented on taking people at their word. Truth is I've lost count of how many times contractors and employees told me a coil was clean when it wasn't. Their warn't lying,they simply didn't see dirt until I showed them how to make certain. I did the same until wiser men showed me different. I still haven't mastered how to perdict what third parties ( mfgr,dealer and distributor in this case) will do. Hopfully you don't need to go that far so let's do what we can on our own before finding out. I just believe this is well worth persuing since it cost's nothing and will do no harm. I can't say the same about tapping into sealed systems. Manys a perfectly charged system has been contaminated,caused to begin leaking or worse when needlessly opened up. As a rule of thumb,as compressors get smaller, sensitivity increases across the board and skill to deal with it become's increasingly neccessary. If not useful on this unit,I have some tips for confined coils. Adapt as the need arises. I carried mirrors including one similar to those dentists and hygeniests use. It's sometimes amazing to see what's around corners. Much quicker than dissassembly only to find everything ok. A garden sprayer will handle most coil wash jobs but in addition I carried pressurized containers with different coil washes inside. I often prefer pushing dirt back out in direction it came from. A 1/8" soft copper pipe with spray head can be snaked into back side of coil and using high pressure liquid or plain air ( depending on whether pressure tank is upright or inverted) can drive dirt out to side I can see. Eventhough you can't see wand and spray head,the spray can be directed by watching dirt come out side which is visiable. I figure this can save tech time and do better work when dealing with M-splits. If a wet vac hose with 90* floor tool can be manipulated to catch dirt and liquid as it's expelled,you can do 1st class on central system coils. Bigger spray head,more water and more pressure. I would use no rinse evap coil cleaner on this ms but it usually only come's in gallons. I have no objection to diswashing or laundry detergent if that's all one has. If you have a digital thermometer that reacts within secounds of temp change, and an amp meter,do this. Watch and record running temp and amps. Do amps increase above rated run amps before compressor cut's off, do temps progressivly change as amps change and other readings. Since I've lead us this deep,I should at least say why I think this could be air flow related. A freeze up caused by low refrigerant can be expected to start iceing at point where it enter's coil then progress until air flow begin's to drop then continue progressivly covering coil in turn progressivly restricting air flow. That's a clean coil with inadiquate refrigerant. A properly charged coil drop's temp rather even across whole coil. A properly (and to a degree, inadiquate) charged coil with inadiquate air flow from dirt restriction or too low fan can be expected to frost then shortly ice across intire coil surface. Anywho,this will be one less thing tech need's to do if one must be called. Your amp-temp chart might also prove helpful.
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junkmailhold
13 years ago
There is not much that you can do about it once you have your system. This is the importance of sizing the equipment properly. If sized properly based on your house's J-load, your system should NOT be cycling every 8 minutes. It sounds like your system is oversized.

The other thing you could have done is gotten a two-stage heat pump which would run at a lower stage to keep the run times longer.

But, unfortunately, there is not much you can do after you have the system except for what neohio mentioned above.
tigerdunes
13 years ago
tedrik

as I recall you have a Goodman system-correct?

check and see what your CFM setting is at your air handler. it is possible to lower CFMs to 350 which in effect removes more humidity. The downside is it could cause a freezeup at your coil and it will reduce your BTU output. However, this may help your situation.

do you even know what your inside RH is?

I think its worth a try if you monitor this.

next option would be another thermostat that has CPH setting and/or perhaps a stat with "dehumidify on demand" feature(with VS air handler).

IMO
tedrik
Original Author
13 years ago
I have a 3 ton heat pump (1585 sq ft house). The inside air handler has multiple settings. I have it set on 1250 CFM. I did notice today at outside temp of 94 degrees that it has been runnning 20 minutes and off for 10 minutes. It's early AM So far with freon added a week ago we're getting cold air and very good airflow. I know it's a matter of time before we have another icing problem due to leak/leaks. Just hope it's a TINY leak and it lasts a couple of years.

I noticed on the tech's invoice he wrote possible coil replacement at $2650 or with warranty $1550 Labor!! He never mentioned the coil-except to say the coil was clean as well as the intake- both-Very clean).
tigerdunes
13 years ago
tedrik

you may have some shortcycling at the lower temps but I would not be concerned about that. your biggest problem is the leak, the typical gas n go service call you received, and the likelihood of a problem in the future at the most inopportune time.

IMO
neohioheatpump
13 years ago
You could probably prevent the short-cycling by programming your thermostat in such a way that it has to 'recover' from a a big temperature difference. That would force it to run for a long period of time.
tedrik
Original Author
13 years ago
After we had the freon added both my wife and I realized that it was never this cold after installation 2 years ago! It was June of 2008 and almost everyday it went to 2nd stage cooling (yellow light on tstat) for at least a couple of hours. Right now, after a week(after bringing it to full charge) it has never gone to 2nd stage (green light stays on). This leads me to believe that it was not fully/correctly charged at installation. It's all about installation-installation-installation!

We are actually thinking about cutting future losses and having a new system installed next year from a reputable company that we know will be around for a long time-and most importantly a 10 year PARTS & LABOR warranty!!

Short cycles bad for compressors?

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Short cycles bad for compressors?

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