frigoblock FK25 SL, refrigerant charge?

[knighty]

I have the back from a truck as a freezer box (temporary use until new freezer finished)

it's a Frigoblock FK25 SL ( http://www.frigoblock.com/en/products/fk-series/fk-25-sl.html )

it's one of the ones where the truck engine has a generator attached and the refrigeration is all electrical, no engine etc.

dataplate says it needs 8.5kg of R410A

it's been vacked out, pressure tested to 500psi with dry nitrogen and then sharged with 8.5kg... but it's running as if under charged?

reluctant to put any more gas in it... anyone know if they need more gas than dataplate shows?

[seanf]

Normally if its just the one evaporator in the overcab package and no additional remote evap coils its just the labelled charge. Maybe you have the phase rotation the wrong way around and the evap fans running backwards giving low pressure. The evap fans also have a motor to blade coupling that can snap.

you may also have a four-way valve for defrost or heating hidden down beside the compressor.

[Brian_UK]

What makes you suspect that is short of gas?

Has the box come down to temperature or us it still in pulldown mode?

[kelvin278]

Is RE. Rear evaporator at the back of the truck if so charge is 12.5kg - 13kg

[charlie patt]

Depends on how many evap I would check size of receiver if its a 16 ltr receiver it's a twin ie 12 kilo if 10.5 ltr 8.5 kilo is the sight glass still in it or been removed ? Check fan rotation for starters

[knighty]

fan rotation is right, there's a sight glass on the receiver with a small green ball in it to show the level, liquid doesen't reach that level - but that level sight glass seams high?

sight glass on the liquid line is pretty dirty, not much use, new one on order

I ripped out all the wiring and re-wired it from scratch with a time clock for defrost, it's working much better now, seamed to stick on defrost before, maybe some other electrical gremlins before too

only using the main/front evap right now, rear evap to be wired in later

still doesen't seam right... if we load up with fresh meat to freeze (5 metric ton, 10,000lb) temp runs about -12'C after 24hours, -14'C 48hours, -16'C 72hours, then -32'C all of a sudden... seams a little odd to me

I appreciate it's overloaded when we load with fresh meat, we expect that, a couple of days to freeze is ok (dog food, meat super fresh)

recovered charge out, vac'd unit out again, charged with 8.5kg fresh refrigerant - I was worried the previous electrical problems meant some strange combination of solenoid valves not opening might have screwed up the previous pressure test / vacuum

[seanf]

You may only see the refrigerant reach that receiver glass if you pump it down and have the correct charge, just depends on what the units doing.

Is it one of those liquid line sight glasses with the drier that screws into the bottom? You might be able to undo the glass part of the sight glass and give it a clean and still be able to seal it back up with the white sealing ring.

The soleniod valves are a bit delicate, if someones forced a coil off the valve stem you can easily bend the stem and it causes the valves to stick open, may not be every time.

If your rear evap is all tubed up and connected to the main unit then youll need to add the additional refrigerant charge.

[knighty]

I was tempted to pump it down and fill till the level in the receiver reached the level glass/green ball - but I was worried that would be over charged

yes liquid line sight glass ontop of the dryer - I'll have a look at cleaning it, it'll have to wait a while because I'll have to recover the refrigerant out of the whole system first - there's a liquid line coming from the receiver with no shut off valve on it :-o

solenoid valves look good, but there's no telling what happened before I got the unit

rear is connected up (and will be put into use later) so guess I do need more refrigerant!

thanks for the help :-)