![background image](http://html1.mh-extra.com/html/carrier/supra-750mt/supra-750mt_operation-and-service-manual_2563856082.webp)
5-4
62--611XX--20 (03/04)
INDICATION / TROUBLE
POSSIBLE CAUSES
REFERENCE
SECTION
5.3.3
Unit operates long or continuously in cooling
Container
Hot Load
Defective box insulation or air leak
Allow time to
pull down
Correct
Refrigeration system
Abnormal pressure
Temperature controller malfunction
5.3.6
5.3.8
Compressor
Defective
4.9
5.3.4
Unit will not heat or has insufficient heating
Refrigeration
Abnormal pressure
Temperature controller malfunction
Hot gas valve malfunction
5.3.6
5.3.8
5.3.11
Compressor
Compressor drive defective
Compressor defective
4.9
4.9
Engine does not develop full rpm
Speed control linkage
Engine malfunction
4.3.4
5.1
5.3.5
Defrost cycle malfunction
Will not initiate defrost
automatically
Defrost thermostats (DTT) open or defective
Loose terminal connections
Air sensing tubes defective or disconnected
Replace
Tighten
Check
Will not initiate defrost manually
Microprocessor defective
Loose terminal connections
Defrost thermostats (DTT) open or defective
Glow/Defrost switch defective
Replace
Tighten
Replace
Replace
Initiates but does not defrost
Hot gas valve malfunction
Defrost relay (DR) defective
5.3.11
Replace
Frequent defrost
Defrost timer to be adjusted
Wet load
2.8.6
Normal
Does not terminate or cycles on
defrost
Defrost thermostats (DTT) shorted closed
Glow/Defrost switch defective
Replace
Replace
5.3.6
Abnormal pressure
5.3.6.1 Cooling
High discharge pressure
Condenser coil dirty
Condenser fan defective
V-belt broken or loose
Discharge check valve restricted
Noncondensibles or refrigerant overcharge
4.16.2
Check
4.4
Replace
Replace
Low discharge pressure
Compressor valves(s) worn or broken
Hot gas valve malfunction
4.9
5.3.11
High suction pressure
Compressor valves(s) worn or broken
Compressor gasket(s) defective
Hot gas valve malfunction
4.9
4.9
2.9.2