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Refrigeration Diagnosis Chart - VIR Valves-In-Receiver System

Observe refrigeration system in areas listed below while engine operates at 2, 000 RPM with control lever in "HI" and temperature dial at 65. All windows should be open and hood should be up. Blower motor should be disconnected when required in chart.

System Condition OBSERVED OPERATING CONDITIONS System Correction
Outlet Air Temp. Sight Glass Head Pressure at Ambient Temperature Evaporator Pressure Evaporator Outlet Pipe Temperature Oil Bleed Line Temperature
Normal 40-50° Clear 70° 80° 90° 100° 28-32 PSIG Cold Warm  
160# 190# 220# 250#
200# 230# 260# 290#
With Blower Lead Off No Air Flow Lower than Normal Maintains Pressure Gets Cold
Refrigerant (1) Charge Low Warm Foamy or Bubbly (4) Lower than Normal Normal to Low Warm Cold Find Leak. Repair and Recharge.
VIR Liquid (1) Pickup Tube Screen Partially Plugged Warm Foamy or Bubbly Low Normal to Low Cool or Warm Cool or Warm Clean Screen and System as Required. Change Desiccant and Recharge.
Refrigerant (1) Charge Lost Warm Clear Very Low Very Low Warm Warm Find Leak. Repair, Change Desiccant and Recharge.
Refrigerant Overcharge Blows Relief Valve on Hot Days Normal Clear High Normal Cold Warm Recharge to the Specified Charge.
X-Valve (1) Diaphragm (2) Discharged Warm Clear Low Low Warm Cold Replace X-Valve Capsule.
Vacuum Loss (1) in STV Capsule Bellows or Valve Piston Stuck Closed Warm Foamy or Bubbly Low High Warm Warm Replace STV Capsule.
STV (1) Stuck (3) Open Cold Evaporator May Ice Up Affecting Air Flow Clear Low Normal to Low (3) Cold Warm Replace STV Capsule.
STV Setting too High Warm Clear Normal High Cool to Warm Cool or Warm Replace STV Capsule.
(1) Superheat Switch May Close and Thermal Fuse link Open to Shut Off the Compressor.
(2) Allow the System to Warm Up and Equalize Before Repeating the Test. If the Condition Doesn't Recur the System has Excess Moisture Causing Ice to Form in the Valve. Discharge the System, Replace the Bag of Desiccant, Evacuate the System for 30 Minutes and Recharge.
(3) Goes to Low Pressure or Vacuum with Blower Disconnected.
(4) May be Bubbly or Clear with Blower Disconnected.
Fig 1: Compressor Electrical Circuit
G09312013Courtesy of GENERAL MOTORS COMPANY
Fig 2: Blower Control Circuit
G09312014Courtesy of GENERAL MOTORS COMPANY
Fig 3: Normal & Low Engine Vacuum
G09312015Courtesy of GENERAL MOTORS COMPANY
Fig 4: Complete Vacuum Circuit
G09312016Courtesy of GENERAL MOTORS COMPANY
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