Table of Contents
Advertisement
Head Pressure Control [Headmaster]
The Cornelius "I" series remote systems use an Alco Head Pressure
Control, normally referred to as a headmaster. This control is
mounted in the remote condenser with a fan cycling control switch.
Using both these controls gives the system positive operation under
a wide range of condensing temperatures.
The cycling control starts the fan at 270 PSI and stops it at 205 PSI
allowing a positive efficient operation at the high temperature oper-
ating ranges.
The headmaster controls the operation when the condensing tem-
perature drops below 70°F. The "I" series refrigerant charge is HP -
receiver
62 [R - 404A] and the headmaster dome charge setting is 200 PSI
discharge
of nitrogen pressure making it stable under the low temperature op-
erating range down to - 20°F.
The normal flow pattern through the headmaster is from the con-
denser port to the receiver port. When this flow pattern is unable to
maintain a receiver outlet pressure equal to or above the dome
pressure setting of the valve, the dome pressure will force the valve
portage to change closing the condenser port and opening the by-
pass port from the compressor discharge line. This allows the high
condenser
pressure vapor from the discharge port to "buck" the receiver pres-
sure back up. With the condenser port closed, the refrigerant is
above 70°F
backed up in the condenser, basically reducing the condenser size,
normal
assisting in maintaining the discharge portage flow and increasing
the head pressure.
Remember, sense of touch to the lines of the headmaster will deter-
mine the flow path the headmaster is in, condenser to receive, or
bypass to receiver.
High side gauge installed at the receiver outlet valve will determine
if the headmaster is functioning to maintain the proper operating
pressure.
In the event the control appears to be "stuck in bypass", the pres-
receiver
sure drop across the headmaster must be measured. With a gauge
discharge
installed at the receiver outlet valve and the high side service valve,
the pressure difference at these two points must be less than the 15
PSI. The three most common causes of an excessive pressure drop
are shortage of refrigerant, kinked remote lines, and excessive line
length.
Eliminate refrigerant shortage first. Add refrigerant in two-pound in-
crements (not to exceed six pounds) to determine if it corrects the
condenser
pressure drop. If pressure drop is not corrected, inspect line set for
sharp bends or kinks and correct as required. If adding refrigerant
does not correct continued (bypass) condition and line set is not
below 70°F by-pass
damaged, replace headmaster.
19
630460004
Advertisement
Table of Contents
