Low Oil Flow Screw Chillers

Issue:

• There is no specific value for oil pressure in the GP2 compressors used in the Pueblo Air Cooled and Water Cooled Chillers. Oil Protection for helical rotor compressor is accomplished through monitoring Intermediate Oil Pressure and System Differential Pressure.  This Oil loss/flow protection is done by monitoring the pressure as reported by pressure transducers in the condenser, compressor and the evaporator. 
• RTAC / RTAE
  • The intermediate oil pressure transducer for this compressor was out of the acceptable pressure range for 15 seconds, while the Delta Pressure was greater than 35 PSID.
  • Acceptable range is 0.50 > (PC-PI) / (PC-PE) for the first 2.5 minutes of operation, and 0.25 > (PC-PI) / (PC-PE) thereafter.
• RTHD / RTAF
  • The intermediate oil pressure transducer for this compressor was out of the acceptable pressure range for 15 seconds, while the Delta Pressure was greater than 15 PSID.
  • Acceptable range is 0.50 or 0.60 > (PC-PI) / (PC-PE) for the first 2.5 minutes of operation, and 0.40 or 0.50 > (PC-PI) / (PC-PE) thereafter.
    • The higher ratios used if the system DP is less than 23 PSID.
• RTWD
  • The intermediate oil pressure transducer for this compressor was indicating an unacceptable oil pressure drop as a % of the available oil pressure to move oil, suggesting significantly reduced oil flow to the compressor.
    See spreadsheet for Oil Pressure drop and Oil Filter Life Calculation.
  • Acceptable Oil Pressure Drop Ratio < 0.3 + (.0005 * Oil_Flow_Forcing_DPcktx ) + ( 3.8 / SqRoot(Oil_Flow_Forcing_DPcktx)) for first 2.5 minutes of operation.
  • Acceptable Oil Pressure Drop Ratio < 0.2 + (.0005 * Oil_Flow_Forcing_DPcktx ) + ( 3.2 / SqRoot(Oil_Flow_Forcing_DPcktx)) after 2.5 minutes of operation.

Resolution:

1. Validate MP software on controller is up to date.
2. Validate oil return and supply lines are opened.
3. Validate accuracy of all the 3 sensors.
   1. PC = Condensing Pressure (oil separator)
   2. PI = Intermediate Oil Pressure (compressor)
   3. PE = Evaporator Pressure (evaporator suction line)
4. Use spreadsheet to determine integrity of the oil filter.  Replace oil filter as required. Refer to the product specific spreadsheet below.
   1. Refer to RTAC-SVD02B-EN for GP2 compressor servicing information. Oil Filter, Check Valve, Motor Terminal, Piston, etc.
5. Validate there is no restriction in the oil return line and confirm the Y-strainer is clean.
6. WATER COOLED ONLY: RTHD, RTWD, RTUD
   1. Validate master oil valve operation (RTHD only).
   2. Validate gas pump operation.
   3. Validate optical oil loss level sensor operation.
   4. Differential pressure required to facilitate oil movement (investigate condenser vs evaporator water temperatures).
   5. Validate condenser water regulating valve (if installed).
7. Validate oil charge and level.
   1. May need to transfer oil from evaporator to oil separator, allow time to boil off (energize heaters), then check level.  Refer to IOM and/or Service Guide for oil level checks.
   2. Low oil could be an early hint of oil migration, the EXV having trouble controlling superheat (carry over), and a possible noisy compressor.
8. Validate pressure drop across evaporator.  Flow needs to be above minimum.
9. Liquid level sensor mis-operation - top mounted liquid level sensors are an improvement to the bottom mount sensors.
10. Allow chiller to run and trip on diagnostic, then capture the Data Recorder files and Chiller Service Report to try to determine root cause of failure.

Notes:

Other Considerations:

• Restriction in oil cooler or oil supply line - check for pressure differential
• Kepner valve malfunction (check valve in compressor)
• Compressor operation (load, unload, stepper valve operation)
• Low loads can contribute to this condition
• Chiller operating off of the operating map 

Resources Available:

• Tech TV Video(s):

• Reference Literature:
  (Electronic copies can be pulled from e-library at Trane Residential (tranetechnologies.com))
  • IOM: RTAC-SVX-1P-EN, RTHD-SVX01H-EN, RLC-SVX09L-EN (RTWD), RTAF-SVX001H-EN, RTAE-SVX001C-EN
  • Service Guide: RTAC-SVG003C-EN, RTHD-SVG002B-EN, RLC-SVG002B-EN (RTWD), RTAF-SVG001G-EN, RTAE-SVG001C-EN
  • Service Bulletin: RTAC-SVD02B-EN (CHHP Compressor Service and Troubleshooting Bulletin)
  • Service Bulletin: RLC-SVD05A-EN (Diagnostic Troubleshooting Bulletin)
• Other:
  • N/A

Other Question/Problem/Cause Statements:

• Low Oil Flow
• What should be the minimum oil pressure on the compressor?
• How to change the oil filter in an RTAC Compressor?
• How to change the oil filter in a CHHP Compressor?
• How to change the oil filter in a GP2 Compressor
• How to change the oil filter?
• RTAC Oil Filter Change?
• RTHD Low Oil Flow Worksheet?
• RTHD Low Oil Flow?
• RTAE Low Oil Flow?
• RTAF Low Oil Flow?
• How could I check if I need to replace the oil filter?
• When should I change the oil filter?
• Low Oil Flow; CH530

Facts:

• RTAC
• RTHD
• RTWD
• RTUD
• RTAF
• RTAE
• Air-Cooled Chiller (Pueblo) (RTAC)
• Water-Cooled Chiller (Pueblo) (RTHD)
• Air-Cooled Chiller (Charmes) (RTAC)
• Water-Cooled Chiller (Pueblo) (RTWD)
• Water-Cooled Chiller (Pueblo) (RTHD)
• Air-Cooled Chiller (Pueblo) (RTAF)
• Air-Cooled Chiller (Pueblo) (RTAE)

Document Identifier: DOC-76888

WARNING:

Information in this article is intended for use by individuals possessing adequate backgrounds of electrical and mechanical experience and who comply with all federal, state, and local laws, rules, orders, or regulations related to the installation, service, or repair of a heating or central air conditioning product. Any attempt to install, service, or repair a heating or central air conditioning product may result in personal injury and/or property damage. The manufacturer or seller cannot be responsible for the interpretation of the information contained herein, nor can it assume any liability in connection with its use.