Is HVAC Cycling Too Often? (AC)

[npalen]

Wondering if my house AC is cycling too often? (short cycling) The attached photo is a screenshot off my tablet which is running an app called "Intelligent Clamp Meter". The app connects via bluetooth with an amp probe attached at the house breaker panel.

The left column is amps and the timeline across the bottom showing a start of about 7:15 AM. The AC is a Lennox two stage which runs about nine or ten amps on Hi cool and about six or seven on Lo cool.
We've been having days in the 90F high temp and the AC doesn't normally get into Hi cool until the afternoon.

The stage one and stage two differential is set to 2.0 degrees but I never see the temp vary more than one degree from the set temp while the compressor is cycling as shown in the pic.

The five year old Lennox unit is a 36,000 BTU with inverter air handling cooling a 1600 square foot ranch style well insulated

Edit: As you can see, the unit cycled on four times between about 7:00AM thru 10:00AM with an outside temp of 75F to 80F. Thermostat is set to 73F.

 

[tallyho8]

It looks like it is cycling just right to me with more off time than on time. I like a unit that keeps the temp within 1 degree and runs for a short amount of time instead of a unit that lets it heat up 2 or 3 degrees and then runs for a long time.

 

[KennyG]

Looks fine. The better thermostats have options to cycle on different temperature gains. Keeping the variation low is usually better. It improves comfort by keeping humidity more consistent. The only time you will get into a short cycle problem is if you have an air supply blowing directly on your thermostat. I would guess yours is properly located.

 

[npalen]

My concern was that it was wasting energy by having to restart the compressor so often. It is a 16 seer unit so maybe that is not the case. I do appreciate the knowledgeable feedback.

 

[kenmac]

Looks fine. The better thermostats have options to cycle on different temperature gains. Keeping the variation low is usually better. It improves comfort by keeping humidity more consistent. The only time you will get into a short cycle problem is if you have an air supply blowing directly on your thermostat. I would guess yours is properly located.

My VRF Never, or hardly ever cycles on and off. It keeps a constant temp through the day, or night no matter the ambient temp.
It idles on low cool at about 15 HZ. and will ramp up if needed.

Most regular thermostats have a 2 deg. swing before cycling the unit on/off

 

[Dftodd]

Short cycling is pretty obvious if your outside next to the unit. Inside it will seem like everything is normal with the air handler running.

Outside the unit will start up, run for 30 seconds to a minute, shut down, then immediately start back up.

 

[KennyG]

My VRF Never, or hardly ever cycles on and off. It keeps a constant temp through the day, or night no matter the ambient temp.
It idles on low cool at about 15 HZ. and will ramp up if needed.

Most regular thermostats have a 2 deg. swing before cycling the unit on/off

I've not seen VRF in a residence although I understand they exist. Do you have ductwork or is each room individually controlled?

 

[kenmac]

I've not seen VRF in a residence although I understand they exist. Do you have ductwork or is each room individually controlled?

Mine is connected to duct just like a conventional system (one to one)

The smaller unit is for upstairs which we never use the up stairs So, I decided to just keep the Trane until it quits

 

[Sigarms]

I've not seen VRF in a residence although I understand they exist. Do you have ductwork or is each room individually controlled?

The issue it seems now is terminology as to what people actually mean by Variable Refrigerant Flow.

As far as a heat pump simultaneously heating and cooling at the same time with multiple indoor heads, the only thing I know that exist is 3 phase (some single phase out there, but they can not heat and cool at the same time with multiple indoor units).

I'd love to see a true residential heat pump VRF in single phase, but I have no doubt that when they first hit the market (which they will sooner or later), they will be so out of line price wise, most people will pass on them (as is commercial jobs are slowly coming down after 5-10 years in the field, but they are still higher than anything else out there).

As is now, even for conventional residential use multi zone mini splits, I try to stay away from having to use a branch box in existing homes.

Because Kenmac stated that his system is a 1 to 1 using a ducted air handler, I don't believe it's the "VRF" system you're thinking about used in commercial applications.

 

[Sigarms]

Wondering if my house AC is cycling too often? (short cycling) The attached photo is a screenshot off my tablet which is running an app called "Intelligent Clamp Meter". The app connects via bluetooth with an amp probe attached at the house breaker panel.

The left column is amps and the timeline across the bottom showing a start of about 7:15 AM. The AC is a Lennox two stage which runs about nine or ten amps on Hi cool and about six or seven on Lo cool.
We've been having days in the 90F high temp and the AC doesn't normally get into Hi cool until the afternoon.

The stage one and stage two differential is set to 2.0 degrees but I never see the temp vary more than one degree from the set temp while the compressor is cycling as shown in the pic.

The five year old Lennox unit is a 36,000 BTU with inverter air handling cooling a 1600 square foot ranch style well insulated

Edit: As you can see, the unit cycled on four times between about 7:00AM thru 10:00AM with an outside temp of 75F to 80F. Thermostat is set to 73F.

Get an app that Lennox uses to monitor their equipment. A two stage compressor in the summer, as I read the graph, should not be coming on and turning off within the hour.

That said, I'm an idiot so I may be reading the graph you posted incorrectly. If the app is stating the drop between stages, you would seem fine IMO.

Long story short, if you had the unit for 5 years, go to your electric bill and see how it varies. Could be some other variables at play, but that's where I would start. If it's outrageously high next bill, you have an issue somewhere. If it's the same, the app is haywire.

Not certain what inverter air handling cooling exactly is. I doubt you have a inverter air handler, most likly perhaps on the outdoor unit, which means it's not an XP16 unit.

 

[Sigarms]

It looks like it is cycling just right to me with more off time than on time. I like a unit that keeps the temp within 1 degree and runs for a short amount of time instead of a unit that lets it heat up 2 or 3 degrees and then runs for a long time.

If you're using a two stage compressor and the load is sized correctly for the equipment size, you WANT more run time than off time. The power usage is in starting the unit, not running it continuously 24/7.

 

[bnold]

Based on the information provided only the 1st stage is cycling on and off.

4 cycles within 3 hours is nothing to be concerned about and certainly not short cycling.

Wouldn’t have any worries about that run time.

I splurged on 2 variable speed compressor, variable condenser fan and variable evaporator fan, multi-zone Trane units include the new house. 7 zones in the house, I’ve been very satisfied with the units.

Units at cost, or I would have likely gone a different route as they are still pricey at cost!!

 

[Sigarms]

Based on the information provided only the 1st stage is cycling on and off.

If a system is sized properly using a two stage compressor outdoor unit in the middle of summer, and the 1st stage is cycling on and off (per the outdoor unit being on and off), I would be a little worried if it happened every hour. If the house it that well insulated, I'd be curious as to the load cal for the house to see the actual numbers. Generally, for AC for cooling, the load is done around in the 90's outside air temp (depending on location) for AC, at a 72-74F indoor temp.

2nd stage compressor is used to the maximum rated BTU/h allowed for cooling. Lots of times you don't need the maximum cooling, and this is where a two stage compressor offers you an advantage by only running in first stage.

All that said, we're basing our diagnosis off an unknown app that may or may not have anything to do with the HVAC equipment. If the electric bills are within norm, I'd guess the information off the app is incorrect.

EDIT - Might of missed it, but how long has the OP been using the app and how has it differed over time in the past per cycling?

 

[Jimatunes]

It looks like nothing is wrong with this particular system, but you better ask a technician to look at it carefully. I know many guys that graduated from one of these https://www.onlytradeschools.com/hvac/ trade schools and are good HVAC technicians now. There are a lot of them in every more or less big city or town, and you will not have a problem finding one. I know that it is always better to have a recommendation from a friend or just a person you know so you can be sure that one or another contractor will do their job carefully. You can ask the people you know whether they can recommend a good HVAC technician, and I’m sure they will be able to help you.

 

[tractortroof]

Cycling has to do with current outdoor load conditions and house insulation. Manual J loads are designed so that the system can handle the upper and lower extreme conditions, so during shoulder seasons every system is oversized.

2-stage helps that out, zoning also. But under low load conditions a system will do all kinds of short cycling. What do you keep the set point at?

 

[tractortroof]

Oops thread necromancy

 

[5030]

Most regular thermostats have a 2 deg. swing before cycling the unit on/off

Which is adjustable I hope you realize. Short cycling is usually indicative of low refrigerant level.

 

[Dftodd]

Which is adjustable I hope you realize. Short cycling is usually indicative of low refrigerant level.

To much/little freon, or a bad pressure valve.

I've had short cycles due to too much freon or a bad pressure valve.

Started out with a bad pressure valve. AC company topped up the freon based on ambient temperature after replacing the pressure valve.

When a heat wave came through, the system started short cycling again. That was caused by too much freon in the system for the temperature.

They bled off a little freon and then we were good.

The unit at work would turn into a solid block of ice when it got low on freon and was switched to heat

Tech would have to switch it to cool and let the outside unit thaw for an hour or so before they could get the door off to top up with freon

 

[Sigarms]

They bled off a little freon and then we were good.

There is so many things wrong with this statement that I don't know where to begin

The bigger question is if the system was overcharged, why?

That said, a system over 10-15 years old, I can understand why it may be losing it charge over time.

 

[Dftodd]

There is so many things wrong with this statement that I don't know where to begin

The bigger question is if the system was overcharged, why?

That said, a system over 10-15 years old, I can understand why it may be losing it charge over time.

There was a long story. When we bought the house, the fan motor went out due to a faulty pressure sensor inside and the unit short cycling.

Tech did a bush fix on the fan to get us back up and running till the correct fan motor came in. He had to drain and recharge the system when he replaced that sensor.

Tech promptly forgot about it I ran into the tech in town about 6 months later (middle of winter and really cold) and reminded the Tech about the fan.

So he ran out and replaced it. Apparently gave the system a top up on freon as well and got it a little heavy.

Didn't have an issue till Satan decided to show up with 130° temperatures in August (6 months after the top up).

Was working fine the week before with 110° to 120° temperatures.