Table of Contents
Advertisement
32
D - Refrigeration System
At the earliest stage of development work on
R-134a, tests were carried out on a different type of
synthetic oil known as Poly-Alkaline Glycol (PAG).
This oil is also used in certain air conditioning
systems for cars. PAG and Ester oil DO NOT mix
with one another. Service equipment used for
R-134a / Ester oil must not come into contact with
PAG.
Water In The Refrigeration
System
Even in very small quantities, water in any
refrigeration system can cause the following
problems:
• Ice plugs in capillary tubes.
• Copper plating in compressor.
• Reactions with organic materials in systems.
• Corrosion of metals.
R-134a and Ester oil will aggravate the problem
of water in the refrigeration system. Ester oil may
react with water vapor and is hydroscopic (it will
absorb water if it comes in contact with humid air).
Water is also more soluble in R-134a than R-12.
To minimize the water content whenever service
work is performed, the refrigeration system should
always be thoroughly evacuated through process
tube adaptors on both the high and low sides of
the system. Evacuation must be for a minimum
of 30 minutes to at least a 29.9 inch (500 micron)
vacuum.
Vacuum
Inches Hg.
28.940
29.530
29.832
29.882
29.901
29.915
29.917
29.919
VACUUM CHART
Boiling Point
Microns
of Water °F
25000
77.9
10000
52.0
4600
32.0
1000
1.0
500
-11.2
150
-32.8
100
-38.2
50
-49.0
To achieve the required 29.9 inch (500 micron)
vacuum, a properly maintained two-stage vacuum
pump in good condition is required. A two stage
pump can reach a deeper vacuum than a single
stage because the exhaust from the first pumping
stage is discharged into the second pumping stage.
This means the second stage begins pumping at a
lower pressure so a lower ultimate vacuum can be
achieved (See 2-Stage Vacuum Pump, Figure E3).
2-Stage Vacuum Pump
Figure E3
Vacuum Pump Maintenance
It is absolutely essential to maintain your vacuum
pump according to the manufacturer's instructions
including required oil changes at the recommended
intervals. Vacuum pump oil should always be
changed after evacuating a contaminated system.
Vacuum pump performance should be checked
periodically with a micron gauge.
Vacuum pump suppliers may or may not
recommend changing the vacuum pump oil to the
same type that's in the system being evacuated.
Some manufacturers may recommend a vacuum
pump that's dedicated to R-134a systems.
Robinair has stated that their current and
discontinued vacuum pump models, using mineral
oil currently specified for use in their vacuum
pumps, can be used to evacuate R-134a/Ester oil
systems. Robinair also states that it is acceptable
to alternate between evacuating R-12/mineral oil
and R-134a/Ester oil systems without adversely
effecting the vacuum pump's performance.
For other brands of vacuum pumps, check with the
manufacturer for restrictions and guidelines when
using with R-134a.
Advertisement
Table of Contents
