Condenser fan turns off and on frequently

[ZeroTolerance]

I have a RTU that runs a walk in freezer and one of the condenser fans is attached directly to the contactor while the other fan is attached to a pressure limit switch? When the unit is running the fan connected to the conatactor runs non-stop until the unit suffices itself and the contactor shuts off. The other fan kicks on and off at different times when the unit is running. Sometimes it will rnu for approximately 30sec then kicks off then a minute or so later will kick on again and so on. Is this normal?

[avico]

I have a RTU that runs a walk in freezer and one of the condenser fans is attached directly to the contactor while the other fan is attached to a pressure limit switch? When the unit is running the fan connected to the conatactor runs non-stop until the unit suffices itself and the contactor shuts off. The other fan kicks on and off at different times when the unit is running. Sometimes it will rnu for approximately 30sec then kicks off then a minute or so later will kick on again and so on. Is this normal?

Ha~~~
It's very normal, believe me
Bcz, your fan was controlled ON/OFF by a pressure switch
Your fans will be only working when Temp. and Pressure in Condenser RAISE up to set point. Ok, when temp. and pressure in system go down to stable point, it's OFF
And then....

[little turtle]

I have a RTU that runs a walk in freezer and one of the condenser fans is attached directly to the contactor while the other fan is attached to a pressure limit switch? When the unit is running the fan connected to the conatactor runs non-stop until the unit suffices itself and the contactor shuts off. The other fan kicks on and off at different times when the unit is running. Sometimes it will rnu for approximately 30sec then kicks off then a minute or so later will kick on again and so on. Is this normal?

Rights,
It's normal....fan ON-OFF by pressure sense in the condenser to maintain condensing pressure.
It's not good if condensing pressure is too low or too high.

[Grizzly]

I have a RTU that runs a walk in freezer and one of the condenser fans is attached directly to the contactor while the other fan is attached to a pressure limit switch? When the unit is running the fan connected to the conatactor runs non-stop until the unit suffices itself and the contactor shuts off. The other fan kicks on and off at different times when the unit is running. Sometimes it will rnu for approximately 30sec then kicks off then a minute or so later will kick on again and so on. Is this normal?

As the above guys say, the type of condenser fan control used is not unusual.
I would defiantly attach some gauges and check at what pressure the second fan is being brought in at.
At first read of your post, I would agree with you the condenser fan cycling in and out as you describe is not good.
It would be well worth further investigation. Don't forget to check how clean the condenser coil is as well.
I cannot criticise the first fan being controlled by the compressor contactor as this may well be as designed.
But it may be worth adding this to some form of pressure control, as well as the second fan.
You need to create some "lift" across the comp on start up.

As the above guys say, the type of condenser fan control used is not unusual.
I would definitely attach some gauges and check at what pressure the second fan is being brought in at.
At first read of your post, I would agree with you the condenser fan cycling in and out as you describe is not good.
It would be well worth further investigation. Don't forget to check how clean the condenser coil is as well.
I cannot criticise the first fan being controlled by the compressor contactor as this may well be as designed.
But it may be worth adding this to some form of pressure control, as well as the second fan.
You need to create some "lift" across the comp on start up.
Take another look at it and if necessary let us know what the operating temps are.

Cheers Grizzly

[charlie n]

If you can adjust the pressure switch differential, set it at about 2 bar difference. this may reduce the short on/off cycle.

[lana]

Hi there,

As others said, cycling condenser fans is a method for head pressure control.
The fans must be turned on and off so the design condensing pressure is maintained. If condensing pressure is low then TEV will starve the evaporator and suction pressure decreases.
I suggest that you put another pressure switch and attach the other fan to it so both fans can be turned on and off. This helps in winter start and also prevents the condensing pressure to fall when ambient temperature is low.
Cheers