3. Operation
PFC Operation Manual
54
825160-00, revision B
Modes of Operation
This section describes the three different modes of operation of the PFC.
Stand
is in STANDBY, the C
circulates (and cools) the refrigerant i
refrigerant is not pumped to the cryos
ant is coldest when the unit is operating
ause it has the least h
Cool
t into COOL, the COOL so
refrigerant is pump
cryosurface and returns through the r
e refrigeration
es the heat
system to repeat the process.
DEFROST,
solenoid valve opens. Hot refrigerant
refrigerant warms the cryosurface and
switches to STANDBY when the cryosurface reaches a setpoint temperature and has defrosted.
FC/PFC and PFC/P
The PFC/PFC and PFC/P function in the same way as the PFC. However, the refrigerant is split
into two separate feed and return lines so that it services two cryosurfaces.
In a PFC/PFC, both refrigerant circuits can be put into defrost mode.
In a PFC/P, the "P" circuit does not have an independent DEFROST mode. Only the "PFC"
circuit can be defrosted quickly.
When one circuit is defrosted while the other circuit is in cool, the circuit in cool will warm up
by up to 20°C. Therefore, the timing of defrost must be coordinated so as to maintain your
process requirements. If the second circuit is a baffle for a diffusion pump, this is normally not a
problem. However, when both circuits cool cryocoils, you must evaluate the impact on your
process when you defrost one circuit while the other circuit is in cool during your deposition
process.
If the refrigerant circuits are operated in different modes, the following will happen.
STANDBY versus COOL
The cryosurface being cooled will get several degrees colder than when both cryosurfaces are
cooled simultaneously. This is because there is less total heat load on the system. It is not
possible, however, to get 100% of the cooling capacity into one circuit simply by not using the
other circuit.
Continued next page
by
When the unit
OOL and DEFROST solenoid valves are closed. The unit
n the “stack” in the top of the refrigeration unit. The
urface. The refriger
in this mode bec
eat load.
When the unit is pu
valve closes. Cold
lenoid valve opens and the DEFROST solenoid
ed into the feed line. The cold refrigerant cools the
eturn line to the refrigeration unit. Within th
unit, the refrigerant releas
it absorbed at the cryosurface, and is pumped through the
Defrost
When the unit is put into
the COOL solenoid valve closes and the DEFROST
is pumped from the stack into the feed line. The hot
returns through the return line. The unit automatically
P
