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06-01-2012, 05:09 PM #1
High and low pressure switch in air-cond
Hi Everyone;
I quite new to this, i was wondering how the pressure switch work in air-cond?
Is the pressure switch work like fuse when it sense the limit of low or high pressure in a an air-cond. It why high and low pressure is connected this way?1.JPG
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06-01-2012, 06:08 PM #2
Re: High and low pressure switch in air-cond
Hi and welcome to the forum.
Yes, your assumption is correct, in the event of either switch operating the compressor will be stopped to prevent possible damage to the machine.
The low pressure will monitor the system for low pressure faults, such as refrigerant leakage or perhap a blockage. If the pressure gets too low then the compressor may overheat due to lack of suction gas cooling.
The high pressure does a similar job. The pressure could rise to a too high level due to the condenser being dirty, or the condenser fan failing or even problems with the refrigerant mix if someone has been careless when working on the system. Also if the pressure stays too high the oil may be overheated when it will begin the break down and contaminate the refrigerant. This can lead to motor burn outs.Brian - Newton Abbot, Devon, UK
Retired March 2015
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06-01-2012, 10:46 PM #3
Re: High and low pressure switch in air-cond
Hi, and congratulations on providing information on what you're asking!
Nice to see someone asking for help that is helping everyone to help them for a change.
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07-01-2012, 07:35 AM #4
Re: High and low pressure switch in air-cond
Thank for the detail. So can i connect the low and high pressure in series way to compressor? When compressor is "on" the pressure switch also "on"? Another question, does the compressor keep toggle between "on" and "off" while the toggle time is set by timer?
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07-01-2012, 06:37 PM #5
Re: High and low pressure switch in air-cond
the pressure switch is wired in series with the anti cycle timer-when the timer is asking for the compressor to run the pressure switch will power the contactor coil(low voltage circuit)then the compressor runs-any problems with the fridge circuit and the contactor will de energise and the compressor will stop
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08-01-2012, 05:40 AM #6
Re: High and low pressure switch in air-cond
Thx install monkey, i got another problem how is the compressor in an air cond work? As i mention from my previous post , does the compressor keep toggle between "on" and "off" using anti cycle timer in a period of time which set by the timer?
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08-01-2012, 10:26 AM #7
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Re: High and low pressure switch in air-cond
Nope!
Compressor operation is called by room temperature thermostat. Anti cycle timer is one of conditions which must be satisfied to allow compressor working called by thermostat.
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08-01-2012, 03:44 PM #8
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08-01-2012, 03:57 PM #9
Re: High and low pressure switch in air-cond
Not quite, the anti-recycle timer is often used to prevent the compressor starting too frequently.
Every time a compressor starts the is heat added to the motor winding due to the starting load of the motor. After the compressor has started the motor is cooled by the incoming refrigerant vapour in the suction pipe; this cooling take a little while.
If the compressor was stopped and started in quick succession then it is likelt that the motor will not get cooling properly and eventually overheat causing damage to the motor windings.
Most modern air conditioning unit, for example, will delay the compressor start by 3 minutes. Larger compressors, in chillers etc, may well have a maximum allowance of six starts per hour.Brian - Newton Abbot, Devon, UK
Retired March 2015
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08-01-2012, 04:21 PM #10
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08-01-2012, 04:22 PM #11
Re: High and low pressure switch in air-cond
Ok as you have explain, i dont quite understand how the compressor start running cause what i have see on the diagram it look like the timer is controlling the compressor to start and to off. For example i set my timer 5 minute and let the compressor run , does it mean that it will run 5 minute and then off it 5minute and then run back in 5minute?
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08-01-2012, 10:33 PM #12
Re: High and low pressure switch in air-cond
Last edited by Brian_UK; 08-01-2012 at 10:46 PM. Reason: Wrong terminal number used.
Brian - Newton Abbot, Devon, UK
Retired March 2015
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08-01-2012, 10:50 PM #13
Re: High and low pressure switch in air-cond
Then the short cycle timer locks out the control circuit should there be any attempt by the thermostat to start the compressor again within 5 minutes. After 5 minutes, timer then closes the control circuit and compressor is free to start when required, so long as pressure switches are also closed.
To the optimist, the glass is half full. To the pessimist, the glass is half empty.
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08-01-2012, 11:44 PM #14
Re: High and low pressure switch in air-cond
Thanks Mike, good addition to cover my ommission.
Brian - Newton Abbot, Devon, UK
Retired March 2015
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09-01-2012, 12:24 AM #15
Re: High and low pressure switch in air-cond
Ok,let summary back again. It mean that the anti short cycle timer is to delay the compressor start when the thermostat is on. The compressor will continue on till the thermostat is off and in the same time it also block compressor on back within 5 minute when thermostat is on? I hope i get it right
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09-01-2012, 12:36 AM #16
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09-01-2012, 09:01 AM #17
Re: High and low pressure switch in air-cond
Thx guys i solve it already. I need some advice on phase protector.phase proctetor.JPG
This the phase protector i using. I need it to be connect in this way.
example.JPG
The phase protector have 6 pin (RST and ABC) , i not quite sure how it work. Can anyone explain it to me?
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09-01-2012, 10:32 PM #18
Re: High and low pressure switch in air-cond
OK, so the thermostat and anti-restart problem is resolved.
The phase protector works by sensing whether the three phases are connected correctly, i.e. U,V,W.
If any two phases are swapped then the protector will keep the control circuit open.
The reason for the reverse phase protection is to protect rotation sensitive machines from running the wrong way.Brian - Newton Abbot, Devon, UK
Retired March 2015
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09-01-2012, 10:56 PM #19
Re: High and low pressure switch in air-cond
Looks like R S T go to the phases and A B C are for the control circuit to turn the compressor contactor off in the event of a fault with the supply.
Not sure if A B C are live in and out and a alarm contact or live in and out and a neutral like the kirwan phase protectors as your diagram is not clear.
Just trace the wires on the diagram and see where they go. Or phone the manufacturers tech dept.Mostly found in Oxfordshire, UK :)
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09-01-2012, 11:02 PM #20
Re: High and low pressure switch in air-cond
its a common ,no,nc contact-stick 415v on and test continuity on a to b or c to work out ur control circuit,also disconnect the 415v to prove the contact breaks also-carefully and safely
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10-01-2012, 09:03 AM #21
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10-01-2012, 11:26 PM #22
Re: High and low pressure switch in air-cond
Yes, power supply to pin C, switch contacts B & C
Brian - Newton Abbot, Devon, UK
Retired March 2015
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10-01-2012, 11:34 PM #23
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25-01-2012, 11:59 PM #24
Re: High and low pressure switch in air-cond
if you wiring phase rotation relay as per wiring diagram the only power going to relay is the 3 phases, the nuetral is being switched,saying that if phase relay is open then you will have control power to relay but nuetral when closed.
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26-01-2012, 12:04 AM #25