Installation
Moisture obstructs the proper functioning of the
compressor and the refrigeration system.
Air and moisture reduce service life and increase
condensing pressure, and cause excessively high
discharge temperatures, which can destroy the
lubricating properties of the oil. Air and moisture
also increase the risk of acid formation, giving
rise to copper platting. All these phenomena
can cause mechanical and electrical compressor
failure.
For these reasons it’s important to perform a
vacuum dehydration on the system to remove
all residual moisture from the pipe-work after
assembly;
MLZ and MLM compressors are delivered with
< 100 ppm moisture level. The required moisture
level in the circuit after vacuum dehydration
must be < 100 ppm for systems with an MLZ and
< 300 ppm for systems with an MLM compressor.
• Never use the compressor to evacuate the
system.
• Connect a vacuum pump to both the LP & HP
sides.
• Evacuate the system to a pressure of 500 μm Hg
(0.67 mbar) absolute.
• Do not use a megohm meter nor apply power
to the compressor while it’s under vacuum as
this may cause internal damage.
Vacuum evacuation and
moisture removal
Refrigerant charging
It is recommended that system charging be
done using the weighed charge method, adding
refrigerant to the high side of the system.
Charging the high and low sides of a system
with gas simultaneously at a controlled rate is
also an acceptable method. Do not exceed the
recommended unit charge, and never charge
liquid to the low side.
Vacuum or charge from one side can seal the
scrolls and result in a non-starting compressor.
When servicing, always ensure that LP/HP
pressures are balanced before starting the
compressor.
Be sure to follow all government regulations
regarding refrigerant reclamation and storage.
Liquid line filter driers
A properly sized & type of drier is required.
Important selection criteria include the driers
water content capacity, the system refrigeration
capacity, and the system refrigerant charge.
The drier must be able to reach and maintain
a moisture level of 50 ppm end point dryness
(EPD). Danfoss recommends DCL (solid core)
driers for the MLM compressor (R22 with
Alkylbenzene) and DML (100% molecular sieve)
driers for MLZ compressors (R407A,R407F,R404A,
R507, R134a, R22) with PVE oil.
For servicing of existing installations where acid
formation may be present, the Danfoss DCL solid
core filter drier containing activated alumina is
recommended.
After burn out, remove & replace the liquid
line filter drier and install a Danfoss type DAS
burnout drier of the appropriate capacity. Refer
to the DAS drier instructions and technical
information for correct use of the burnout drier
on the liquid line.
Insulation resistance and
dielectric strength
Insulation resistance must be higher than 1
megohm when measured with a 500 volt direct
current megohm tester.
Each compressor motor is tested at the factory
with a high potential voltage (hi-pot) that
exceeds the UL requirement both in potential
and in duration. Leakage current is less than 0.5
mA.
MLZ/MLM scroll compressors are configured
with the pump assembly at the top of the shell,
and the motor below. As a result, the motor
can be partially immersed in refrigerant and
oil. The presence of refrigerant around the
motor windings will result in lower resistance
values to ground and higher leakage current
readings. Such readings do not indicate a faulty
compressor, and should not be cause for concern.
In testing insulation resistance, Danfoss
recommends that the system be first operated
briefly to distribute refrigerant throughout the
system. Following this brief operation, retest the
compressor for insulation resistance or current
leakage.
Never reset a breaker or replace a fuse without
first checking for a ground fault (a short circuit to
ground). Be alert for sounds of arcing inside the
compressor.
44
FRCC.PC.015.A8.02
Application Guidelines
