Section 12-00: Climate Control System—Service
1994 Mustang Workshop Manual
SERVICE PROCEDURES

Refrigerant System Tests

The best way to diagnose a concern in the refrigerant system is to note the system pressures (shown by the manifold gauges), and the A/C clutch cycle rate and times. Then compare the findings to the values shown in the following charts.

 

Important—Test Requirements

The following test conditions must be established to obtain accurate pressure readings:

NOTE: When ambient temperature exceed 38°C (100°F), engine should be run at normal idle speed only. For tests in ambient temperatures between 38°C (100°F) and 43°C (110°F), system performance pressures will be the same as those for ambient. Temperatures shown on the chart in the 32°C (90°F) to 38°C (100°F) range. Center A/C register discharge temperatures will also be similar to those shown in the chart in the 32°C (90°F) to 38°C (100°F) range.



Normal A/C Evaporator Core Orifice Cycling A/C Clutch Refrigerant System Pressure/Temperature Relationships




The following test conditions must be established to obtain accurate pressure readings:



Normal A/C Clutch Cycle Rates and Times—A/C Evaporator Core Orifice System




The following procedure is recommended for achieving accurate diagnosis results in the least amount of time:

  1. Connect a manifold gauge set or equivalent, to the system. Purge air from red and blue hoses using system pressure 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.

  1. Start engine and turn ON A/C system.
  1. As soon as the system is stabilized, record the high and low pressures as shown by the manifold gauges. Normally the suction pressure should decrease to a range between 152-193 kPa (22-28 psi) and the A/C cyclic switch (19E561) should open. When the A/C cyclic switch opens, the suction pressure should start to rise to a range between 276-324 kPa (40-47 psi). Somewhere between 276-324 kPa (40-47 psi), the A/C cyclic switch should close and the suction pressure should start to drop.

    The discharge (high) pressure should operate the reverse of the suction pressure. When the suction pressure is dropping, the discharge pressure should increase. When the suction pressure is increasing, the discharge pressure should decrease.

  1. Determine the A/C clutch cycle rate per minute (A/C clutch on time plus off time is a cycle).
  1. Record A/C clutch off time in seconds.
  1. Record A/C clutch on time in seconds.
  1. Record center A/C register discharge temperature.
  1. Determine and record ambient temperatures.
  1. Compare test readings with previous applicable charts.

    If the point where the two lines cross on each of the charts falls within the dark band, the system is operating normally. If the lines cross outside the dark band on one or more of the charts, there is a concern and the specific cause must be determined. This is easily done by using the Refrigerant System and Clutch Cycle Timing Evaluation Chart.

    Additional cause components are listed for poor A/C compressor operation or a damaged A/C compressor condition at the bottom of the following evaluation chart.



Refrigerant System Pressure and A/C Clutch Cycle Timing Evaluation Chart For A/C Evaporator Core Orifice Cycling A/C Clutch Systems
HIGH (DISCHARGE) PRESSURE LOW (SUCTION) PRESSURE A/C CLUTCH CYCLE TIME COMPONENT—CAUSES
RATE ON OFF
High High Continuous Run Continuous Run Continuous Run A/C Condenser Core—
Inadequate Airflow
High Normal to High Continuous Run Continuous Run Continuous Run Engine Overheating
Normal to High Normal Continuous Run Continuous Run Continuous Run Refrigerant Overchargea Air in Refrigerant Humidity or Ambient Temp Very Highb
Normal High Continuous Run Continuous Run Continuous Run A/C Evaporator Core Orifice—
O-Rings Leaking/Missing
Normal Normal Slow or No Cycle Long or Continuous Normal or No Cycle Moisture in Refrigerant System Excessive Refrigerant Oil
Normal Low Slow Long Long A/C Cyclic Switch—Low Cut-Out
Normal to Low High Continuous Run Continuous Run Continuous Run A/C Compressor—Low Performance
Normal to Low Normal to High Continuous Run Continuous Run Continuous Run A/C Suction Line—Partially Restricted or Pluggedc
Normal to Low Normal Fast Short Normal A/C Evaporator Core—Low or Restricted Airflow
Normal to Low Normal Fast Short to Very Short Normal to Long A/C Condenser Core, A/C Evaporator Core Orifice or A/C Liquid Line—Partially Restricted or Plugged
Normal to Low Normal Fast Short to Very Short Short to Very Short Low Refrigerant Charge
Normal to Low Normal Fast Short to Very Short Long A/C Evaporator Core—Partially Restricted or Plugged
Normal to Low Low Continuous Run Continuous Run Continuous Run A/C Suction Line—Partially Restricted or Pluggedd A/C Cyclic Switch—Sticking Closed
Erratic Operation or A/C Compressor Not Running — — — A/C Cyclic Switch—Dirty Contacts or Sticking Open.
Poor Connection at A/C Clutch Connector or A/C Cyclic Switch Connector
A/C Electrical Circuit Erratic—See A/C Electrical Circuit Wiring Diagram
ADDITIONAL POSSIBLE CAUSE COMPONENTS ASSOCIATED WITH INADEQUATE A/C COMPRESSOR OPERATION
A/C Compressor Drive Belt — — — — A/C Compressor Drive Belt Loose
A/C Clutch — — — — A/C Clutch Slipping
A/C Compressor Clutch Field Coil — — — — A/C Compressor Clutch Field Coil Open—Shorted, or Loose Mounting
Control Assembly Switch — — — — Control Assembly Switch—Dirty Contacts or Sticking Open
A/C Clutch Wiring Circuit — — — — A/C Clutch Wiring Circuit—High Resistance, Open or Blown Fuse
A/C Compressor Not Operating — — — — A/C Compressor Operation Interrupted by PCM
ADDITIONAL POSSIBLE CAUSE COMPONENTS ASSOCIATED WITH A DAMAGED A/C COMPRESSOR
A/C Cyclic Switch — — — — A/C Cyclic Switch—Sticking Closed or A/C Clutch Seized
A/C Dehydrator and Receiver Tank — — — — A/C Suction Accumulator Drier Tank—Refrigerant Oil Bleed Hole Plugged
Refrigerant Low — — — — Refrigerant Leaks
a A/C compressor may make noise on initial run. This slugging condition is caused by excessive liquid refrigerant.
b A/C clutch may not cycle in ambient temperatures above 27°C (81°F) depending on humidity conditions.
c Low pressure reading will be normal to high if pressure is taken at suction accumulator/drier and if restriction is downstream of service access valve.
d Low pressure reading will be low if pressure is taken near the A/C compressor and restriction is upstream of service access valve.

The 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 suction pressure and A/C clutch cycle rate while meeting the conditional requirements from previous charts to ensure the condition has been corrected.

In ambient temperatures above 27°C (81° F), the A/C clutch will not normally cycle off. This will depend on local conditions and engine/vehicle speed. Also, A/C 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 A/C clutch will not engage for A/C compressor operation. A rapid cycling A/C clutch is usually an indication that the system is low on refrigerant.

The following tests cover: burned-out fuses, loose wire connections, damaged wires, or collapsed hoses.

 

Checking for A/C Leaks

Attach the manifold gauge set. Leave both manifold gauge valves at the maximum clockwise (closed) position. Both gauges should show approximately 483-551 kPa (70-80 psi) at 24°C (75°F) with engine not running. If very little or no pressure is indicated, leave the vacuum pump valve closed, open the Refrigerant 134-a cylinder valve and set the low-pressure (suction) manifold gauge valve to the counterclockwise position. This opens the system to cylinder pressure.

 WARNING: GOOD VENTILATION IS NECESSARY IN THE AREA WHERE A/C LEAK TESTING IS TO BE DONE. IF THE SURROUNDING AIR IS CONTAMINATED WITH REFRIGERANT GAS, THE LEAK DETECTOR WILL INDICATE THIS GAS ALL THE TIME. ODORS FROM OTHER CHEMICALS SUCH AS ANTIFREEZE, DIESEL FUEL, DISC BRAKE CLEANER OR OTHER CLEANING SOLVENTS CAN CAUSE THE SAME CONCERN. A FAN, EVEN IN A WELL VENTILATED AREA, IS VERY HELPFUL IN REMOVING SMALL TRACES OF AIR CONTAMINATION THAT MIGHT AFFECT THE LEAK DETECTOR.

Check all systems connections, the compressor head gasket and shaft seal for leaks using a good leak detector. Pass leak detector along underside of all points being checked. Refrigerant is heavier than air and will show most readily in those locations.

R-134a Manifold Gauge Set




 

Leak Detector, Electronic

Use Rotunda R-134a Halogen Leak Detector 161-R0010 or equivalent.

The electronic leak detector is operated by moving the control switch to the ON position. The detector automatically calibrates itself when it is turned on. Move the probe at approximately 25mm (1 inch) per second in the suspected area. When escaping refrigerant gas is located, the ticking/beeping signal will increase in ticks/beeps per second. If the gas is relatively concentrated, the signal will be increasingly shrill. Follow the instructions included with the detector to improve handling and operating techniques.

Leak Detector—Electronic