OFFICIAL PARTS SUPPLIER
from 110 degrees to 70 degrees, plus or minus 3 degrees, in less than 30 minutes after system engagement for 30-, 35-, and 40-foot buses.
BTU Capacity Considerations • Gross capacity (most typically used) uses the weakest link (lowest capacity) among the evaporator, condenser and compressor to determine overall system capacity.
• Net capacity (rarely used and difficult to mea- sure) uses multiple simultaneous equations until the system is balanced.
There is neither a universal BTU (British Thermal
Unit) capacity rating method currently being used in the bus air conditioning industry, nor any governing association to police the industry! BTU is the amount of heat required to raise the
temperature of one pound of water by one degree Fahrenheit. Aside from the technical definition of BTU, bus air conditioning system BTU capacity is dependent on many variables. It requires that spe- cific rating conditions be defined for each system component, since each has its own capacity. Capacity ratings can change, higher or lower,
depending on the rating conditions that are being used. So be aware that system BTU ranking is the lowest of the three component values: Compressor, condenser and the evaporator rating Theoretical BTU/hour system ratings, when using
realistic rating conditions at the various vehicle engine/compressor speeds, is a valuable piece of information to assess the application of the system to the vehicle type. However, the best way to measure A/C system
performance is to install an air conditioning system in the vehicle, operate the vehicle into the above mentioned environment, and perform a standard or high-performance, pull-down test. This will then tell you that the air conditioning system you ordered to do the job is the one you got. ●
PLUS All Major A/C Brands COMPRESSOR OIL CAPACITY
When replacing the A/C compressor or any A/C system component it’s important to replace any compressor oil lost during parts change. A low oil level can starve the compressor for oil and lead to compressor failure. BEWARE: Do not overfill too much oil will hinder cooling performance. General guidelines for replacing oil when changing components:
• Accumulator • Compressor • Condenser • Evaporator • Hoses
-
- -
-
2.0oz 1.4oz 1.0oz 2.0oz
- 1.0oz • Receiver drier - 1.0oz
The total oil added to compensate for parts replacement should NEVER exceed total oil capacity for system. It’s
always recommended to follow OEM recommendations.
Bob Pudlewski is the technical editor for School Transportation News magazine and has over 40 years of experience in the school bus industry. He retired as vice president of fleet operations, procurement and maintenance from Laidlaw and is a member of the NTSA Hall of Fame.
4802 W. Colonial Drive | Orlando, FL. 32808 Phone: 866-349-6928
buspartsexperts.com See Us At TSD Booth 623
BPE_0319_FP.indd 1
www.stnonline.com 23
2/18/19 9:34 AM
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