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Failure Cause 4
Lack of Oil / Oil Return
There are 4 aspects to correct compressor lubrication.
MOUNTING ANGLE
The compressor must be mounted in accordance with recommendations. Maximum mount angles must not be exceeded.
Oil Quantities
The correct amount of oil must be maintained in the system. Long hose runs and dual evaporator systems must have additional oil added to the system. Severe oil starvation problems may result from insufficient system oil being allowed.
There are two methods of determining oil charge rates for systems — Compressor specific and generic calculation.
Compressor specific calculation
The following chart is a sample (UP/UX200 — Bus application). Compressor and / or system manufacturers charts simular to the one shown below may be referred to for oil calculation.
Passenger Vehicles Only
Cooling Capacity |
Passengers |
Oil quantity in system |
14,000 kcal/h |
60 |
Approx. 1600 cc |
10,000 kcal/h |
4 40 |
Approx. 1100 cc |
|
7,500 kcal/h
|
30
|
Approx. 850 cc
|
|
5,000
|
20
|
Approx. 650 cc
|
Generic Calculation
Total oil capacity of the system should equal 20% of the system refrigerant charge.
EXAMPLE 1 : If a system holds 0.75Kg of refrigerant, then 750 X 20% = 150cc of oil. The UP/UX150 already has 160cc; therefore no additional oil is required.
EXAMPLE 2 : If a system holds 2Kg of refrigerant, then 2,000 X 20% = 400cc of oil. The UP/UX200 already has 180cc; therefore 400 - 180 = 220cc of additional oil is required.
Oil Separators
Oil separators are strongly recommended in multiple evaporator systems due to oil circulation rate reduction and in systems where it is deemed the suction may go below zero. (ie high speed operation).
Oil Separator  |
Accumulator
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Oil separators provide protection in long hose run multi evaporator systems particularly if there is a change of sub zero refrigerant temperatures in high speed operation |
Accumulators hold large quantities of oil. 60ml must be allowed if they are incorporated into the system.
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MISCIBILITY / SOLUBILITY
Only recommended refrigerants and oils are to be used. Failure to comply with this may result in dramatically reduced oil circulation rates with subsequent starvation of the compressor. Warranty is void if non approved oils and refrigerants are used.
In low temperature applications (ie freezer vans) oil quantity and selection must be in accordance with system manufacturers recommendations.
FAILURE CAUSE 5
System Cleanliness (Contamination)
The system must be maintained free of both solid particulant and chemical contamination. Solid particulant contamination will cause direct compressor damage and starvation of the pump due to blocked system filters and screens.
Chemical contamination can reduce solubility / miscibily of refrigerants and oils, reduce lubricity, cause acid etching and sludge formation.
System flushing prior to compressor Fitment
Contaminated systems must be flushed prior to fitting of the new compressor. Individual component flushing is strongly recommended in systems where solid particulant contamination is present (ie previous compressor failure.
Compressors, TX Valves, Pressure Control Valves, Receiver Driers / Accumulators and Mufflers / Pulsation Dampers must not be flushed.
Additional Text — Flushing
For Full details of flushing options / procedures refer to "flushing of Automotive Air Conditioning Systems" — Policies, Procedures and Recommendations.
Additional Procedures — Flushing
In systems where residual contamination is suspected a post fitment inspection service (including a filter / drier replacement) must be conducted to reduce the risk of premature compressor failure. Additionally a "catch all" filter may be used for further protection — refer to commercial refrigeration suppliers for more information.
Failure cause 6
Overspeed
When fitting any compressor from the UNICLA range ensure the compressor driven speed does not exceed the specified limit. This includes both continuous speed and momentary speed as applicable. Crank to compressor drive ratios must not exceed 1.2:1 in normal applications. In low speed governed applications the gearing ratio may exceed 1.2:1 to provide maximum performance providing the rated compressor speed is not exceeded.
Normal Cut Off Sensor Required
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Failure Cause 7
Incorrect Direction of Rotation
Ensure the direction of rotation of the compressor matches the application in which it is being placed. UNICLA compressors are designed to operate in both clockwise (cw) and counterclockwise (ccw) directions however the clutch design varies dependant upon direction of rotation (D.O.R.)
Later generation rubber clutches are designed to operate in both directions making the compressor and clutch assembly multi directional.
Failure to match the clutch with it’s D.O.R. may result in premature clutch failure especially in applications of high torque engagement spike (high head pressure) and / or constant high speed cycling.
Compressor Selection
- Three major factors to take into account
- Direction of rotation (CW or CCW)
- Maximum speed of compressor — calculated by maximum engine speed x drive ratio. (as previously discussed) (use an overspeed cut sensor if required).
- Capacity either shown in graph or table form aligning r/min with compressor capacity.
Interpreting Capacity Data
When selecting compressors or upgrading systems to larger capacity or dual evaporators the compressor sizing (capacity) must match the system.
Compressor selection must be done on the following basis. (basic guidelines only)
- What is the operational speed of the compressor? (Varies dramatically highway to city cycle)
- What is the total net refrigerating capacity of the system? (evaporator rating)
- What refrigerant is being used in the system?
From these 3 basic questions a compressor selection can be made — presuming that the evaporator capacity is adequate for the application the correct compressor can be selected.
Note: Graphs will often incorporate 3 plots onto one grid — power consumption, refrigerating capacity and coefficient of performance (COP) which relates to input (power consumption) verses output (refrigerating capacity). If interpreting single plot graphs ensure you have selected the Refrigerating Capacity Graph. (see sample below)
For single evaporator applications the compressor must cater for the net refrigerating capacity of the evaporator at nominated operating speeds.
For dual evaporator units the compressor must cater for the net refrigerating capacity of all evaporators.
This is the refrigerating capacity graph — must match system capacity. |
The power consumption graph shown here relates to input (drive) power — not capacity. |
Service Checks
If the system has been upgraded (ie dual evaporators) with the compressor undersized for the evaporator loads the technician will often recognise a higher than normal low side pressure. (The inability to pull down the low side). The undersized compressor (with its high suction pressure) is producing an Inadequate Flow of Refrigerant with a high saturation temperature (poor "chilling off" of the evaporator).
Both Factors place serious limitations on the evaporator performance. An inadequate flow to absorb maximum heat from the environment and an evaporator operating at a higher temperature.
Driving Conditions
Customer complaints often indicate adequate highway performance but poor city cycle performance. This condition clearly indicates a compressor with inadequate performance at low speed (see above). A higher capacity compressor is required if the normal driving condition is city cycle. Alternatively a higher compressor speed may be used (drive ratio changed). Providing the compressor maximum speed is not exceeding under any driving conditions.
COPYRIGHT (c) ALL RIGHTS RESERVED. REPRODUCTION OR TRANSMISSION BY PRINTED, , ELECTRONIC OR OTHER MEANS STRICTY PROHIBITED WITHOUT THE WRITTEN PERMISSION OF UNICLA/SCA Australia PTY LTD. |
