Airedale v31xd-at low suction pressure on start up

Just repaired a leak on 1 circuit on an airedale closed control unit charged with 15kg of r407c to 10k of subcooling and is now running with 7k of superheat, air on 20 degrees c and air off 5 degrees c, unit has a tev and has 2 separate circuits with 2 x 15kw coils. The compressors are copeland scrolls with 2 remote condensers as the compressors are in the indoor unit.
Here is the problem.
Upon start up the head pressure before the tev struggles before the compressor has sucked the gas out of the evaporator causing the lp alarm to trigger but only when the temp drops below 0 outside when it is above 0 it goes down to about 1.5 bar before stabilising after about 30 seconds then the system runs perfectly.
What solution could be done,
Pipe run is 40 metres so 80 metres of discharge line in total.
Can the compressor be changed to 2 stage compressor ?
Electronic tev ?
Move the condenser nearer to indoor ?
Any thoughts
Thanks in advance.
MATT.

Classic fault with R407C in low ambients.

On the old Hitachi and Toshiba condensing units we used to install a timer across the LP switch set to 90secs so that, on start up, the LP was bypassed until system stabilised.

You may need to adjust timer settings to suit your system if you decide to go a similar way.

Try it with a temporary switched bypass (light switch or similar) across the LP

Is there any condenser fan speed control , do the fans ramp up to full speed on start up

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Originally Posted by frank

Classic fault with R407C in low ambients.

On the old Hitachi and Toshiba condensing units we used to install a timer across the LP switch set to 90secs so that, on start up, the LP was bypassed until system stabilised.

You may need to adjust timer settings to suit your system if you decide to go a similar way.

Try it with a temporary switched bypass (light switch or similar) across the LP

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Thanks Frank never thought about putting a timer on the LP switch, I did think about putting a ranco one on it and setting it a bit lower than the factory fitted one.

Quote:

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Originally Posted by redroge

Is there any condenser fan speed control , do the fans ramp up to full speed on start up

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I messed with the fan speed control so it only goes into low speed and cuts in at 18 bar and out at 14.
I rang Airedale for a manual on it but they were useless,
I understand the terminal screw for cut in and out but there is another dial on the top right hand corner of the board that seems to effect the speed but without a manual I am a bit lost.

You could also install a Ranco type thermostat set around 8C into the Delay Off timer feed to ensure that the timer is only in circuit when ambients are low.

Here's a link to a little project I rebuilt a while ago that was on R407C where I installed an LP bypass and a HG injection http://www.refrigeration-engineer.co...-your-installs