On some GM applications the high side service port is located past the condenser and before the orifice tube on the liquid line. This makes diagnosing by gauges deceiving. Usually, the high side port is found before the condenser. With the port in front of the condenser, it gives you a more accurate understanding of what the pressure truly is going into the condenser. With the high side after the condenser, you could show a pressure reading that is false, because the condenser could be partially blocked. Therefore, the only reading you are getting is what is exiting the condenser.
The correct way to diagnosis this type of system, with the service ports so close together, is through temperature testing:
- Check the temperature at the inlet and outlet of the condenser. *An acceptable temperature differential is 30°-50°F .
- A low temperature differential could mean an airflow problem, such as bad cooling fans
or restricted air flow.
- A high temperature differential could mean an internal restriction in the condenser.
Remember: on late model systems the condenser cannot be flushed and must be REPLACED