Refrigerant System Performance Check

REFRIGERANT SYSTEM

R-134a System
The major components of R-134a A/C systems are similar to those used previously on Ford R-12 fixed orifice tube type systems. R-12 and R-134a components are similar in design and function. As a result, all Diagnosis and Testing procedures for R-12 components can be used for R-134a components. However, it is very important to note that R-134a system components can only be replaced with other R-134a components. R-134a components cannot be replaced with components used with R-12 systems. The same is true for R-12 components, they cannot be replaced with R-134a components.

CAUTION: R-12 and R-134a components are not interchangeable. Do not replace components from an R-134a system with components for an R-12 system. Also do not replace components from an R-12 system with components from an R-134a system. Mixing components from these two types of systems may cause component failure and damage to the A/C system.

Pressure/Temperature Relationship:

Clutch Cycle Timing Rate:

The best way to diagnose a condition in the refrigerant system is to note the system pressures (shown by the manifold gauges) and the clutch cycle rate and times. Then, compare the findings to the Pressure/Temperature Relationship and Clutch Cycle Timing Rate charts.
^ The system pressures are low (compressor suction) and high (compressor discharge).
^ A clutch cycle is the time the clutch is engaged plus the time it is disengaged (time on plus time off).
^ Clutch cycle times are the lengths of time (in seconds) that the clutch is ON and OFF.

The following procedure is recommended for achieving accurate diagnosis results in the least amount of time.
1. Connect a manifold gauge set, part of Rotunda Air Conditioning Service Kit 063-00010 or equivalent, to the system. Purge air from red and blue hoses by loosening fittings at gauge set. Open only long enough for air to escape and then tighten fittings.

NOTE: The test conditions, specified at the top of each chart, must be met to obtain accurate test results.

2. Start the engine and turn ON A/C system.
3. As soon as the system is stabilized, record the high-and low-pressures as shown by the manifold gauges. The low side should cycle between approximately 24.5 and 40-47 psi. As low pressure drops, high pressure should rise. When the clutch disengages, the low side should rise and the high side should drop.
4. Determine the clutch cycle rate per minute (clutch on time plus off time is a cycle).
5. Record the clutch OFF time in seconds.
6. Record the clutch ON time in seconds.
7. Record the center register discharge temperature.
8. Determine and record the ambient temperatures.
9. Compare the test readings with the applicable Pressure/Temperature Relationship and Clutch Cycle Timing Rate charts.
a. Plot a vertical line for the recorded ambient temperature from the scale at bottom of each chart to the top of each chart.
b. Plot a horizontal line for each of the other test readings from the scale at LH side of the appropriate chart.
10. Disconnect the electrical connector at the clutch cycling pressure switch and remove the switch from the switch fitting.
11. Install a new clutch cycling pressure switch and O-ring on the Tee-Adapter Tool. Leave it on the adapter as a permanent part of the tool. Be sure to lubricate the O-ring before installation.

Tee Adapter Tool Installation:

12. Install the Tee Adapter Tool on the clutch cycling pressure switch fitting and tighten it securely.
13. Connect the low-pressure hose of the manifold gauge set to the side fitting of the Tee Adapter Tool.
14. Connect the electrical connector to the clutch cycling pressure switch on the Tee Adapter Tool.
With the Tee Adapter Tool installed in this manner, the refrigerant system can be operated under normal conditions with clutch cycling pressure switch control and evaporator (suction) pressure can be observed. This will give a more accurate low-pressure reading than can be obtained from a low-pressure gauge port located in the suction line or near the the compressor.

After completing the service, disconnect the manifold gauge set from the Tee Adapter Tool. Disconnect the electrical connector from the clutch cycling pressure switch on the tool and remove the tool from the pressure switch fitting. Install the removed clutch cycling pressure switch and connect the electrical connector.

NOTE: Always replace the protector caps on the gauge port valves after servicing the refrigerant system.

Pressure/Clutch Cycle Timing Evaluation Chart:

At the bottom of the Refrigerant System Pressure and Clutch Cycle Timing Evaluation Chart, additional cause components are listed for poor compressor operation or a damaged compressor condition.

These diagnosis charts provide the most direct and sure way to determine the cause of any concern in a poorly performing refrigerant system.

After servicing and correcting a refrigerant system concern, take additional pressure readings and observe the clutch cycle rate while meeting the conditional requirements of the Refrigerant System Pressure and Clutch Cycle Timing Evaluation Chart to ensure the concern has been corrected.

In ambient temperatures above 38° C (100° F), the compressor clutch will not normally cycle off and in many instances, the clutch will not cycle off when temperatures are above 32° C (90° F). This will depend on local conditions and engine/vehicle speed. Also, clutch cycling will normally not occur when the engine is operating at curb idle speed.

If the system contains no refrigerant or is extremely low on refrigerant, the clutch will not engage for compressor operation. A rapid cycling compressor clutch is usually an indication that the system is low on refrigerant. Refer to Pinpoint Test A: Insufficient Or No A/C Cooling-Fixed Orifice Tube Cycling Clutch System Diagnosis chart. Insufficient Cooling Diagnosis