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pianotuna's avatar
pianotuna
Nomad III
Aug 06, 2022

duty cycle on roof air conditioner

Hi all,

I'm visiting a friend and wanted to see what the duty cycle was on their roof air conditioner. Each cycle was allowed to run twice. For each pair, the second number is the run time. Location is Longwood Florida.

The unit is a 5th wheel with one slide. 30 amp a fifth wheel cougar 33 feet from 2008. One roof air equipped with a device that starts the fans, then cuts in the compressor about 12 seconds later. The opposite happens when the roof air shuts down, i.e. compressor shuts down and then the fan.

I just discovered that the "dump" valve on the air conditioner was open. It is about 5 feet from the thermostat. For the next series of measurements I'll have it closed.

So far:

Ambient temperature 83 f (28.3 c)

Rv temperature 69 f (20.6 c)

duty cycle 5 minutes off and 9 minutes on

raised interior temperature to 70 f (21.1 c)

time to next cycle 8 minutes

duty cycle 5 and 8 (no change--odd)

raised interior temperature to 71 f (21.6 c)

time to next cycle 5 minutes

duty cycle 3 minutes and 5 (???) 2nd cycle was 5 and 3 3rd cycle is 4 and 7

At end ambient temperature was 87 f (30.5 c)
more data to be added later
  • afidel's avatar
    afidel
    Explorer II
    Aug 07, 2022
    Not sure what thermostat they have, but I've got a Honeywell installed in my RV now and one of the advanced parameters I setup was 5 cycles per hour with a 5 minute minimum guard period. This does a good job of balancing dehumidification, temperature swings, noise, and wear on the compressor.
  • time2roll's avatar
    time2roll
    Nomad
    Aug 07, 2022
    Hardly even warm. No wonder it cycles. Come west and mine will often kick on at 8AM and run continuous to maybe 4am and then a few cycles before the sun comes up and back on all day and well into the night again.
  • pianotuna's avatar
    pianotuna
    Nomad III
    Aug 07, 2022
    afidel,

    It is the OEM thermostat, but it is digital--so state of the art in 2008.
  • valhalla360's avatar
    valhalla360
    Navigator
    Aug 07, 2022
    Questions:
    - What was the starting interior temperature?
    - Was it consistently sunny, cloudy, shady?
    - Details of the rig: 28ft Class C from the signature but how many slides? Were you keeping the door consistently closed? Any out of the ordinary insulation?

    If you started with the interior temperature equal to the exterior ambient temp, these results aren't surprising. Even though it's cooler outside early, you not only have to cool the air inside but also the solid objects in the camper. Later cycles, the interior is already cooled, so you are only fighting the solar gain. Plus, since you are raising the thermostat setting, it's keeping the temperature differential limited.
  • 3_tons's avatar
    3_tons
    Explorer III
    Aug 07, 2022
    This is all anecdotal, fails to consider a wide number of variables including humidity - no two individual scenarios will produce the same result…Honestly, what is one to conclude??… I don’t really get the objective of this thread, but then again, I suspect the thread itself is the only objective…

    3 tons
  • pianotuna's avatar
    pianotuna
    Nomad III
    Aug 07, 2022
    valhalla360 wrote:
    Questions:
    - What was the starting interior temperature?
    - Was it consistently sunny, cloudy, shady?
    - Details of the rig: 28ft Class C from the signature but how many slides? Were you keeping the door consistently closed? Any out of the ordinary insulation?

    If you started with the interior temperature equal to the exterior ambient temp, these results aren't surprising. Even though it's cooler outside early, you not only have to cool the air inside but also the solid objects in the camper. Later cycles, the interior is already cooled, so you are only fighting the solar gain. Plus, since you are raising the thermostat setting, it's keeping the temperature differential limited.


    This is a friend's rv--a fifth wheel cougar 33 feet.

    Starting temperature was 69 f (20.6) as specified in the original post.

    5th wheel partly in shade

    one slide as specified in original post

    doors closed for entire test

    no extra insulation as far as known

    It is much warmer ambient today but I was not in the 5th to take measurements.

    At 5:44 pm local time ambient is 92 f (33.3 c), high for day was 97 f (36.1 c). Interior of RV is 73.

    No cycling at this time.

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