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HVAC Service Documents

Recommended Charging Procedure
Charge Determination
Basic Troubleshooting
R134a and PAG Oil Handling
Compressor Oil Handling
Compressor Troubleshooting
Blower Motor
Glossary of Common HVAC components

Gauge Diagnostics

Using Gauges for Troubleshooting
Air in cooling system (insufficient suction)
Defective expansion valve
Excessive refrigerant
Insufficient compressor operation
Insufficient refrigerant
Moisture Intrusion
Refrigerant does not circulate

Summary Table of Gauge Diagnostics



Summary Table for Gauge Diagnostics


Low Pressure Side is TOO HIGH
The low pressure side normally becomes too high when the high pressure side is too high.
Cause Inspection Remedy
Defective Thermoswitch The magnetic clutch switch turns off before the outlet air temperature is sufficiently low. Replace the thermoswitch
Poor Expansion Valve
temperature sensor contact
The high and low pressure sides gauge pressures equalize when the magnetic clutch is turned off (within a short time duration) Replace Compressor
Expansion Valve opens too far Frost has adhered to the suction hose / pipe Install the temperature sensor against the low pressure pipe and cover with insulating tape.
Clogged compressor suction filter Compressor fitting is cool but the low pressure hose is not. Remove and clean the filter.

Low Pressure Side is TOO LOW

Cause Inspection Remedy
Insufficient Refrigerant There is little temperature difference between the low and high pressure sides. Repair any leaks and recharge the refrigerant to the correct levels.
Clogged liquid tank
(receiver dryer, accumulator)
Considerable temperature difference between the inlet and outlet sides of the receiver dryer during operation. Also, tank may be frosted Replace liquid tank (receiver dryer)
Clogged expansion valve Expansion valve inlet side is frosted. Generally the low side pressure is near vacuum. Replace expansion valve.
Expansion valve temperature
sensor gas leak
(damaged capillary tube, etc..)
Expansion valve outlet side is chilled and low pressure side is LOW. Clean or replace expansion valve.
Clogged or blocked piping Low pressure readings decrease or a negative reading is shown. Indicates piping is clogged or blocked between the evaporator coil and the compressor. A frost spot may indicate the point of blockage. Clean or replace piping.
Defective thermoswitch
(cold control)
Evaporator is frozen showing ice along the face of the coil, not just frost on the manifolds of the coil. Adjust temperature sensing tube to a cooler part of the coil or replace the thermoswitch.

High Pressure Side is TOO HIGH

Cause Inspection Remedy
Poor Condenser cooling Dirty or clogged condenser fins, Cooling fans do not operate correctly. Clean and / or repair the condenser core / fans.
Excessive refrigerant Verify by gauge reading Utilize your refrigerant recovery equipment to capture excess refrigerant. Charge to the correct refrigerant levels.
Air in the system Pressure is high on both high and low sides Evacuate, vacuum and recharge with refrigerant.

High Pressure Side is TOO LOW

Cause Inspection Remedy
Insufficient refrigerant Little temperature difference between the low and high pressures. Repair any leaks and recharge the refrigerant to the correct levels
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Perrin Manufacturing is committed to providing you with superior products and services; we renew this pledge through continual improvement of our products and motivation of our staff.

We faithfully comply with all of the requirements of our ISO 9001:2008 Quality Management System, the most current edition of the standard. Beyond that, our highly trained quality staff persistently search for new ways to improve the effectiveness of our system.
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