HART 2442 Commercial Refrigeration
#8 Pressure Control Switches
The function of a high- pressure switch is to monitor the discharge pressure of the
compressor and to shut off the compressor if the high side pressure exceeds a pre-
determined level. Its function is also to control head pressure: a high - pressure switch
also turns the fan off and also forces head pressure to go up.
The 4 conditions that can cause high discharge pressure are 1. A dirty condenser 2.
Restricted air flow through the condenser 3. A faulty condenser blower motor 4. If the
system is overcharged. A high discharge pressure is not beneficial to the compressor.
An encapsulated pressure switch is not adjustable. The normal position of the contacts
of a high-pressure switch are closed. Pushing the manual reset button will close the
contacts. In a high pressure switch the cut-out pressure will open the contacts. In a high
pressure switch the cut-in pressure will close the contacts.There are 2 wire leads
included in the structure of an encapsulated high - pressure switch. In a high-pressure
switch cut-out pressure is more than cut-in pressure. The maximum condensing
temperature should not exceed 155 F. The formula for the relationship between cut-in,
cut-out and differential in a high pressure switch is the following: cut-in is cut-out minus
differential. The maximum safe condensing pressure for an R134 system is 275 PSIG.
The maximum safe condensing pressure is 400 PSIG for a R22 system. The maximum
safe condensing pressure for a R404 system is 475 PSIG. The amount of a reasonable
differential setting in a high pressure switch that is adjustable is 50 PSIG. The 2
functions that a low- pressure switch is designed to perform is 1.safety control and
2.temperature control. In a low-pressure switch the cut-out pressure is less than the
#8 Pressure Control Switches
The function of a high- pressure switch is to monitor the discharge pressure of the
compressor and to shut off the compressor if the high side pressure exceeds a pre-
determined level. Its function is also to control head pressure: a high - pressure switch
also turns the fan off and also forces head pressure to go up.
The 4 conditions that can cause high discharge pressure are 1. A dirty condenser 2.
Restricted air flow through the condenser 3. A faulty condenser blower motor 4. If the
system is overcharged. A high discharge pressure is not beneficial to the compressor.
An encapsulated pressure switch is not adjustable. The normal position of the contacts
of a high-pressure switch are closed. Pushing the manual reset button will close the
contacts. In a high pressure switch the cut-out pressure will open the contacts. In a high
pressure switch the cut-in pressure will close the contacts.There are 2 wire leads
included in the structure of an encapsulated high - pressure switch. In a high-pressure
switch cut-out pressure is more than cut-in pressure. The maximum condensing
temperature should not exceed 155 F. The formula for the relationship between cut-in,
cut-out and differential in a high pressure switch is the following: cut-in is cut-out minus
differential. The maximum safe condensing pressure for an R134 system is 275 PSIG.
The maximum safe condensing pressure is 400 PSIG for a R22 system. The maximum
safe condensing pressure for a R404 system is 475 PSIG. The amount of a reasonable
differential setting in a high pressure switch that is adjustable is 50 PSIG. The 2
functions that a low- pressure switch is designed to perform is 1.safety control and
2.temperature control. In a low-pressure switch the cut-out pressure is less than the
