EPA Technicians Only!
- Think SAFETY First
- Don't do these procedures if not EPA certified
Deep Vacuum Conditions
Deep vacuum can cause arcing damage to the Fusite pins.
Models built after September 1991 have an internal vacuum protection
and stop pumping when the pressure exceeds approximate. 10:1. Scroll
compressors should never be used to evacuate a system, allowed to run
in a vacuum or the have the suction service valve closed to check how
low the compressor will pull suction pressure.
Hipot test reading showing high levels of leakage
Scroll compressors are configured with the motor on bottom
and the pumping components at the top. If the motor is immersed in liquid
refrigerant they can show higher level of leakage current. The system
should be run for a brief period of time before the hipot test is conducted.
Green slime in the oil
Green slime is formed when there is a low side leak. This creates high temperatures
which combined with water and air pulled in the system, degrades the
white mineral oil by oxidation and hydrolysis. These degradation products
attack the copper components and create the green oil/slime. Green slime
is more prevalent in systems using a compressor that has a bronze or
other largely copper containing bearing. Install a low pressure control
and fix the low side leak to prevent green slime oil. Use proper refrigeration
clean up procedures to remove the green slime.
Loud, very loud, relief sound coming from the compressor
Some model scrolls have an internal pressure relief (IPR)
valve. This valve opens at a discharge to suction differential of 375
to 450 psi (R-22) or 550 to 625 psi (R-410A). Check for restrictions
in the discharge line, overcharge of refrigerant or a faulty component.
No start after charging
Rapid charging only on the suction side of a scroll system
may cause the scrolls to seal axially. Charge on the low and high side
simultaneously to avoid this situation.
Check the condenser or evaporator fan for proper operation.
Also check for loss of refrigerant charge or re-circulation of the condenser
air. Being that the scroll is a refrigerant cooled compressor, checking
the superheat at the compressor would be beneficial. The recommended
superheat at the compressor is 20 degrees.
Overload tripping, pressures equalized, low amp draw - 3 Phase.
Normally caused by the compressor rotation running in
the reverse direction. There is also an elevated sound associated with
reverse rotation. Reverse any two of the 3 phase power leads and reapply
power. Reverse rotation for over one hour may have a negative impact
on the bearings.
Pressurized while unbrazing
If the refrigerant charge is removed from a scroll by
bleeding the high side only, it is possible for the scrolls to seal
preventing pressure equalization through the compressor. This may leave
the low side shell and suction line tubing pressurized. If a brazing
torch is applied to the low side in this condition, then the pressurized
refrigerant and oil mixture could ignite when it escapes. It is important
to check the high and low side for pressure before unbrazing.
Runs noisily then trips on overload - Single phase.
Brief power interruptions may result in powered reverse
rotation in compressors built before May 1995. This occurs as a result
of the high pressure discharge gas expanding backwards through the scrolls
at the power interruption, causing the scroll to orbit in the reverse
direction. When the power is reapplied while reverse rotation is occurring,
the compressor may continue to run noisily in the reverse rotation for
several minutes until the overload trips. When the protector resets,
the compressor will start and run normally. Installing an electronic
control which can sense brief power interruptions with a five minute
time delay will help avoid this condition.
Short cycling - Off cycle with pump down
Refrigerant is leaking back thru the compressor. Install
a discharge line check valve to avoid short cycling.
Scroll compressors may run backwards for a brief period
at shutoff as the internal pressures equalize. This momentary reversal
of direction of the scrolls has no effect on the compressor durability
and is entirely normal. Single phase compressors built since May 1995
have a device which prevents the reverse rotation and eliminates the
noise. Three phase models have a device which reduces but does not eliminate
The reversing valve should be wired so that the valve
does not reverse when the system is shut off by the operating thermostat
in the heating or cooling mode. If the valve is allowed to do this,
suction and discharge pressures are reversed to the compressor. This
results in a condition of system pressures equalizing through the compressor
which can cause the compressor to slowly rotate until the pressure equalizes.
This condition does not affect the compressor durability.
Suction line noise and vibration
The scroll compressor produces two very close frequencies.
These may result in a low level "beat" frequency which can
be detected as noise coming along the suction line into a house. Elimination
of the "beat" can be achieved by lessening either of the frequencies.
A second situation that may exist is that under some conditions
the normal starting motion of the compressor can transmit an "impact"
noise along the suction line. Three phase compressors may be more pronounced
due to their higher starting torque.
Common remedies for these noises are to add a shock loop
in the suction line, insure that an angled service valve is fastened
to the unit, or add a suction line muffler.
These sounds are not usually associated with heat pump
systems because of the reversing valve and tubing bends that are components
of the system.
Suction pressure does not drop / discharge pressure does not rise
On single phase models, either the reversing valve or
the compressor is faulty.
On three phase models first, reverse any two of the power
leads and reapply power. If the pressures still do not move to normal
values then either the reversing valve or the compressor is faulty.
Start up clearing noises or lock up and trip on the protector several times before starting
Usually occurs when the system charge exceeds the recommended
limit and the compressor fills with refrigerant. A crankcase heater
will help in this situation.
Start up gurgling sound
This condition is just the normal startup of the motor,
or it could exist when there is a low voltage condition. Installing
a factory approved start capacitor and potential relay will help this