Gauge Diagnostics - Perrin Manufacturing

Using Gauges for Troubleshooting

Gauge pressure is the first tool in AC troubleshooting. The table below shows 7 Gauge Readouts that you may encounter. Use the Gauge Readout Tool separately or in combination with the table of Gauge Diagnostics for AC troubleshooting.

Gauge Readout Tool

Normal ConditionsAir in cooling system (insufficient suction)Defective expansion valveExcessive refrigerantMoisture IntrusionRefrigerant does not circulateSummary Table of Gauge Diagnostics

Normal Conditions

1 AtmosphereRoom Temperatures of 30-38 C (86 - 96 F)Engine speed of approx. 1500 rpm or about 75% of rated engine speed

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Air in cooling system (insufficient suction)

Pressure RangeLow side: 36 to 50 psiHigh side: 284 to 356 psiIndicationsBoth pressures are TOO HIGHThe low-side piping is not coldCausesAir in the systemRemedyEvacuate the systemReplenish the refrigerantCheck the gauge readingsIf prolonged operation with air in the system, the liquid tank must be replaced.

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Defective expansion valve

Pressure RangeLow side: 30 to 36 psiHigh side: 313 to 327 psiIndicationsBoth pressures are TOO HIGHCausesImproper refrigerant chargeDefective expansion valveImproper temperature sensor installationRemedyVerify refrigerant chargeCheck temperature sensor installation and insulationIf the refrigerant charge is okay and the temperature sensor installation and insulation are correct then replace the expansion valve.

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Excessive refrigerant

Pressure RangeLow side: 36 to 43 psiHigh side: 327+ psiIndicationsBoth pressures are TOO HIGHCausesPressure increase due to excessive refrigerantInsufficient condenser coolingRemedyVerify the refrigerant levelClean the condenserCheck and adjust the fan belt and / or the condenser fan motors

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Moisture Intrusion

Pressure RangeLow side: 18 to 28 psiHigh side: 85 to 256 psiIndicationsLow pressure side alternates between a vacuum and normal pressureCausesMoisture has frozen in the air conditioner system, clogging the expansion valve.RemedyEvacuate the systemReplace the receiver dryerRecharge the system

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Refrigerant does not circulate

Pressure RangeLow side: 0 to -29.99 psiHigh side: 71 to 85 psiIndicationsLow pressure side becomes a vacuumHigh pressure as listed aboveFrost or condensation on the front and rear pipe connections of the receiver dryer or expansion valveCausesAC system is blocked by contamination or iceAC system is shut off by defective expansion valve or tempeerature sensorAC line from evaporator to compressor has kink in the lineRemedySTOP OPERATION IMMEDIATELYCheck for contamination or iceIf moisture is found then evacuate the systemIf the expansion valve is defective then replace itReplace receiver dryerRecharge with refrigerant to proper levelRepair any kinked hoses

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Summary Table of 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