Copeland scroll tripping

[cadwaladr]

Got a customer who is new to me he has just replaced a condensing unit on his cold store its a brand new Copeland ten horse power he called me I today to help,the fault was after running for about five minutes it stops on internal overload when I got it running the amps draw was not level across the three phases two phases around 12 amps each but one at 14? then found he had wired the crankcase heater to one of the compressor supply phases removed that set it off running again amp draw now level ,discharge pressure low around 130 psi it's on 404a and its been charged liquid then a sound which I could describe as a valve opening in the compressor and the pressure went to around 250 psi it's about a 20degree c ambient here,all was well for about 30 minutes then it stops pumping and tripping again,left it for another hour started it now it's tripping after 5 minutes,the customer said that when he was brazing pipework a sound like something rattling down the pipework! I can only presume this to be something foreign do these compressors have an inlet screen,the old condensing unit was working ok he was just updating as the old was a water cooled condensor.

[cadwaladr]

The model number is zb 76kce tfd 651

[Rob White]

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If you rule out the amperage for the moment, now that they are even,
you say discharge is about 9 bar? what is the suction?
Internal thermal protection tripping? these comps rely on cool gas returning
to the comp to cool the windings so is it possible that there is a blockage
on the suction inlet?

Rob

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[monkey spanners]

The 7.5hp ZR90's rotalock ones had inlet screens. Whats the suction superheat running at? I think these have an internal doodah that stops them pumping so they recycle the same gas then trip on thermal. Theres a sticker on them to that effect.

[Glenn Moore]

Hi Cad
It sounds like this machine has a discharge temperature sensor to protect the machine if the discharge temp goes to high. It called an ASTP , if the discharge goes to high in temperature the sensor forces the scrolls apart to stop the machine pumping, allowing the gas temp to drop or the machine will trip the motor to prevent it burning out. The internal overload can take some time to reset.
Scroll machines are notorious for cooking themselves if the suction superheat at the compressor is too high . The machine must not be allowed to run with a suction pressure less than 2 Bar to prevent scroll damage by the scrolls clashing due to no gas or lube between the scrolls

[cadwaladr]

Thanks for the replies it looks likely the suction may be restricted because this compressor is fitted with the device that parts the scroll having just downloaded the information from Copeland,so tomorrow it's suction inlet to be investigated thanks again friends.

[cadwaladr]

Went back to this today,no gauze/filter in suction-inlet ,oil level was low topped it up now it works a treat the oil was about a third up the sight glass did not realise how critical it was all's well that ends well.