McQuay seasoncon ALP-067A Installation And Maintenance Data page 44

It takes about 120 seconds to warm the heater element enough to open
the bimetallic contact thus allowing time for the pressure differen-
tial to develop.
If during operation, the differential drops below 10 PSI, the heater
element will be energized and the compressor will stop.
can be reset by pushing the reset button on the control.
pressor does not re-start, allow a few minutes for the heater element
and bimetallic contacts to cool and reset the control again.
To check the control, pump down and shutoff all power to the unit.
Remove the compressor fuses, and install a voltmeter between termin-
als "L" and "M" of the oil pressure control.
unit control circuit (separate disconnect or main unit disconnect de-
pending on the type of installation).
stop switch (Sl) is in the "on" position.
should now be energized but with the absence of the compressor fuses,
no oil pressure differential can develop and thus the pressure actu-
ated contacts of the control will energize the heater element and
open the bimetallic contacts of the control within 120 seconds.
this happens, the safety relay is de-energized, the voltmeter read-
ing will rise to 115V , and the compressor contactor should open. Re-
peated operations of the control will cause a slight heat buildup
in the bimetallic contacts resulting in a slightly longer time for
reset with each successive operation.
LINE (SEE NOTE 1)
LINE (SEE NOTE 2)
NOTES:
High Pressure Control
The high pressure control is a single pole pressure activated switch
that opens on a pressure rise to de-energize the entire control cir-
cuit except for compressor crankcase heaters.
pressure and is factory set to open at 380 PSIG and can be manually
reset closed at 315 PSIG.
condenser surface or start the unit with fuses in only one fan fuse
block (FBll) and observe the cut-out point of the control by watch-
ing condenser pressure rise.
out is the cut-out setting of the control.
CAUTION: Although there is an additional pressure relief device in
the system set at 425 PSIG, it is highly recommended that
the "control stop" switch (Sl) be close at hand in case
the high pressure control should malfunction.
page 44
CONTACT
L
1. Hot only when the unit thermostat calls for compressor
to run.
2. Hot only when other safety control contacts are closed.
To check the control, either block off
Check to see that the control
The control circuit
BIMETALLIC CONTACTS
The highest point reached before cut-
The control
If the com-
Turn on power to the
NEUTRAL
NEUTRAL
SAFETY RELAY
It senses condenser
__
When