A/C Refrigerant System Controls, Checking
A/C Refrigerant System Controls, Checking
Pressure relief valve, checking
- Function: Protects refrigerant circuit from excessive pressure.
- The pressure relief valve plug indicates if valve has opened to release pressure - arrow -. An adhesive plate is pushed out.
A/C Pressure Switch F129, checking
Visual check: Ensure that O-ring (color: red) 10.8mm x 1.8mm is seated in groove.
Switch function between contacts -T4a/1 - and -T4a/2- (at connector housing) switches A/C Clutch N25 off whenever:
- excessive refrigerant circuit pressure is present (e.g.: insufficient airflow over condenser or if system is overcharged)
- insufficient refrigerant circuit pressure is present (e.g.: when refrigerant has leaked out).
Switch function between contacts -T4a/3- and -T4a/4- (at connector housing) switches Coolant Fan V7 to 2nd speed when refrigerant pressure rises.
Switching conditions
- Contacts -1- and -2- open below 1.2 bar (17.4 psi) and closed above 2.4 bar (34.8 psi) switching threshold
- Contacts -1- and -2- open above 32 bar (464 psi) and closed below 24 bar (348 psi) switching threshold
- Contacts -3- and -4- closed above 16 bar (232 psi) and open below 12.5 bar (181.2 psi) switching threshold
Switch function, checking
- Bridge contacts -1- and -2- with engine running. If A/C Clutch N25 switches on, refrigerant system may be empty.
High Pressure Sensor G65, function
Where equipped, the High Pressure Sensor G65 transmits a square wave signal to Coolant Fan Control (FC) Module J293 at a rate which varies according to the refrigerant system pressure.
The signal from High Pressure Sensor G65 is processed as follows:
Based on the pulse rate transmitted by the High Pressure Sensor G65, the Coolant Fan Control (FC) Module J293 determines the A/C refrigerant system pressure and controls the function of the A/C Clutch N25 and Coolant Fans accordingly. For example:
- Switches the Coolant Fan V7 to the next higher speed when pressure in the refrigerant circuit increases.
- Switches off A/C Clutch N25 when pressure is excessive (for example when engine cooling is insufficient).
- Switches off A/C Clutch N25 off when pressure is too low (for example with low/no refrigerant).
The signal generated by High Pressure Sensor G65 is also provided as an input to the Motronic Engine Control Module (ECM). As the amount of torque needed to drive the A/C compressor varies according to the refrigerant system pressure, the ECM processes this signal in order to enhance engine performance.
High Pressure Sensor G65, multi-pin connector assignments
- Contact 1: Ground (GND)
- Contact 2: Square wave signal (output) to Coolant Fan Control (FC) Module J293 and Motronic Engine Control Module (ECM) J220
- Contact 3: Terminal 15 (ignition on)
NOTE: A/C Clutch N25 is switched off when connector - B - is disconnected
High Pressure Sensor G65, electrical checks
- Check voltage and ground supply to sensor using wiring diagram.
- Check wiring for short to one another.
- Check wiring for short to B+ and ground.
- Check wiring for short circuit between High Pressure Sensor G65 and Coolant Fan Control (FC) Module J293 using wiring diagram.
- If no wiring faults can be determined, replace High Pressure Sensor G65.
A/C Pressure Switch F129 and High Pressure Sensor G65, removing and installing
Removing
NOTE: Components can be removed without discharging refrigerant system.
- Disconnect electrical connection to switch/sensor
- Remove by turning switch/sensor - B - counterclockwise (switch/sensor threaded onto refrigerant pipe equipped with Schrader valve).
Installing
- Install in reverse order of removal, noting the following.
NOTE:
- Always replace O-ring seal -A - (10.8; 1.8mm)
- Tightening torque 5 Nm (44 in.lb.)