explanation of defrost cycle

[moondawn]

Hi guys can anyone give a detailed explanation on how general split system units work on defrost ie what process it goes through?

maybe also on vrv/vrf if different


thanks lee

[Brian_UK]

Just how detailed do you want it ?

The cycle reverses, the outdoor fan stops, the evaporator is defrosted. When the terminating thermostat is satisfied then it reverses again and produces more hot air from the indoor unit.

[marc5180]

Do you mean what makes the unit go on defrost?

I would also like to know how different manufactures work and why don't they all just work off the coil temperture sensor on the condensor/evaporator.

I was working on a Daikin packaged unit the other day and the unit wouldn't go on defrost, i spoke to daikin and they said it works of 3 seperate sensors...

[VRVIII]

The following is a description of average small inverter split defrost control which may vary depending on manufacturer.

Defrost will be activated when all 4 items have been met

• Coil temp is less than a preset value
• Ambient temp is less than a preset value
• Compressor accumulated run time since last defrost is greater than a preset value (usually about 45min)
• Compressor continual run time is greater than a preset value (5~10min)

When a defrost has been activated the unit will then,

• Stop compressor
• Fully open expansion valve (equalising high/low pressures)
• De-energise reversing valve
• Stop outdoor fan (indoor fan off or LL)
• Compressor starts (frequency is usually preset)
• Expansion valve opens to preset number of pulses
• Hot gas then defrosts coil
• Defrost will end when a preset coil temp is reached (usually 8~12) or a preset time has been reached or compressor discharge line reaches a preset value
• Compressor stops, system equalises, compressor restarts, reversing valve is energised and unit operates under normal heating mode control.

[nike123]

Hi guys can anyone give a detailed explanation on how general split system units work on defrost ie what process it goes through?

maybe also on vrv/vrf if different


thanks lee

[moondawn]

hi there thanks for the info,

i was just wanting to understand how it all works, so basically the compressor stops and outdoor fan stops, then the reversing valve switches over and then compressor comes on and pumps hot gas into the coil allowing the defrost to happen never really touched on this subject before so thanks for all your input

cheers lee

[Brian_UK]

Basically yes but compressor does not stop during changeover.

[moondawn]

Basically yes but compressor does not stop during changeover.

hi brian

is this in most cases then that the compressor continues to run?
VRVIII posted this above:


When a defrost has been activated the unit will then,
Stop compressor
Fully open expansion valve (equalising high/low pressures)
De-energise reversing valve
Stop outdoor fan (indoor fan off or LL)
Compressor starts (frequency is usually preset)
Expansion valve opens to preset number of pulses
Hot gas then defrosts coil
Defrost will end when a preset coil temp is reached (usually 8~12) or a preset time has been reached or compressor discharge line reaches a preset value
Compressor stops, system equalises, compressor restarts, reversing valve is energised and unit operates under normal heating mode control.

Cheers lee

[Brian_UK]

Fair enough, I was thinking mostly of the smaller heat pumps.

They tend to keep running and dump the liquid into the accumulator.

[moondawn]

Fair enough, I was thinking mostly of the smaller heat pumps.

They tend to keep running and dump the liquid into the accumulator.

thank you its a really good site this really informative thanks all

[reganracelis]

basically defrost in evaporator coil occur when defrost timer not activate depending on the settings/ timer.. if this happen,reset the defrost timer..
if defrost timer are functioning well and you experience defrost/ ice forming in evaporator coil.. adjust the defrost timer or the thermostat setting... maybe it was too low...

[moondawn]

basically defrost in evaporator coil occur when defrost timer not activate depending on the settings/ timer.. if this happen,reset the defrost timer..
if defrost timer are functioning well and you experience defrost/ ice forming in evaporator coil.. adjust the defrost timer or the thermostat setting... maybe it was too low...

hi there was not experiencing a problem was just keen to learn about the process of what happens how the coil defrosts etc

thanks for your input though

[flyinkiwi]

Nike123, I hope you've got comps + modules for the AOT12LFBC and OD fan motors + board for the AOT18 ready and waiting!

[nike123]

Nike123, I hope you've got comps + modules for the AOT12LFBC and OD fan motors + board for the AOT18 ready and waiting!

I really don't understand your humor!

[mchild]

The following is a description of average small inverter split defrost control which may vary depending on manufacturer.

Defrost will be activated when all 4 items have been met

• Coil temp is less than a preset value
• Ambient temp is less than a preset value
• Compressor accumulated run time since last defrost is greater than a preset value (usually about 45min)
• Compressor continual run time is greater than a preset value (5~10min)

When a defrost has been activated the unit will then,

• Stop compressor
• Fully open expansion valve (equalising high/low pressures)
• De-energise reversing valve
• Stop outdoor fan (indoor fan off or LL)
• Compressor starts (frequency is usually preset)
• Expansion valve opens to preset number of pulses
• Hot gas then defrosts coil
• Defrost will end when a preset coil temp is reached (usually 8~12) or a preset time has been reached or compressor discharge line reaches a preset value
• Compressor stops, system equalises, compressor restarts, reversing valve is energised and unit operates under normal heating mode control.

On Daikin VRV-S what parameters are used for the normal defrost setting (temp, time and so forth) and how are those changed are when the quick and slow defrost setting are selected?