Scroll compressor

When wiring a 3 phase scroll compressor it is critical to connect correctly. Is there a way to determine if the phases are connected correctly without having to start the compressor and listening to it.

I'm assuming that it's a hermetic.

There is no way of telling from a static compressor unless you have the manufacturers wiring instructions and you already know the connected phase order.

Most units will have a built in interlock that prevents incorrect phase rotation.

So, you have to start the unit. There are a number of ways to find out.

In descending order of 'correctness' they are:

Method 1 - Obtain a phase rotation meter.
They cost about 20 or 30 quid. Most suppliers will stock one. It's a set of three coloured leads on a small solid state box that you connect to the three phases. It usually comes with a set of LEDs that indicate the direction of rotation. You have a 50% chance of getting it right first time.
You will need the manufacturer to tell you the correct rotation. When you have one of these you will probably use it once in a blue moon.

Method - 2 If you have another unit of the same type, have a look at the connections and wire it the same.

Method - 3 Run it for half a minute with your gauges and ammeter on, then reverse two phases and run it again. The one where the suction, discharge and current don't do much is the wrong way.


Most people will opt for methods 2 or 3, usually the latter.

With a centrifugal compressor, a sight glass is usually privided so that the end of the rotor can be seen. You spin the comp for a few seconds under power and watch the direction.

Despite what the good books say, I'm afraid that it's mostly hit and miss.

good luck

Argus
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Niki Lauda

Argus

It is hermetique
Thanks for the info, very very helpful
May your life be blessed!!!

Im opting for method 3, compressor is a Bristol York ACU type
It does have a sight glass

Best regards

Hi Ayb

I once went to investigate an IMI condensing unit that was reportedly not cooling. It was in a building in the centre of Nottingham that was opened about 15 months previously. The complaint was raised because the room it was serving had a number of electronic boxes fail due to high heat.

When I got there the unit was running (IMI MCU+80) but no heat was coming out of the condenser fan. Put the gauges on and the amp clamp and saw running currents within tolerances but no difference in the pressures. Changed the phase rotation and the system started to cool! 15 months running the wrong way - can you believe that??

I always use a phase rotation device before commissioning a new 3 phase unit - only cost a few quid but really save the guesswork.

Frank

Thank you Aiyub, I appreciate the felicitations in these nasty times it goes a long way.

Franks job reminds me of exactly the same thing I hadwith a Carrier 19 series centrifugal working R 11 many, many years ago in the Gulf.

.....It's amazing what getting the direction right can do for the duty! This thing had been running for a year like that.

Nobody would believe that I travelled 3 days for a 20 minute job!

Argus
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GSX-R1100

Excellent advice, Argus. I might add that scrolls are less sensitive to reverse rotations as compared to screws. So just looking at the gauges during start is entirely adequate.

I am amazed at Frank's example of a scroll running backwards for such a long time. IMI must have one fine lubrication system!:)