A/C Refrigerant System, Servicing
NOTE:
- Before carrying out any work on the A/C refrigerant system, refer to "A/C Refrigerant System, Safety Measures" [1][2]Technician Safety Information
- Except where indicated with *, all system components illustrated must only be serviced or replaced after discharging refrigerant system.
1 - Damper
2 - Refrigerant hose
3 - Refrigerant pipe
4 - Refrigerant pipe
- From receiver drier to expansion valve
5 - High pressure service valve
- Only use Kent Moore ACR4 or equivalent
6 - A/C pressure switch -F129- (4-Pin) or high pressure sensor -G65- (3-Pin)*
- Depending on engine type, refrigerant Systems have either an A/C pressure switch - F129- or high pressure sensor -G65- installed. Refer to appropriate wiring diagram.
- Checking -F129-, refer Fig. 2
- Checking -G65-, refer Fig. 3
- Removing and installing, refer Fig. 4
- Component can be removed without discharging refrigerant system
7 - Expansion valve
8 - Evaporator
- In heater/evaporator unit
- Removing
9 - Refrigerant hose
10 - Refrigerant hose
- From compressor to condenser
11 - Condenser
- Removing and installing Service and Repair
12 - Pressure relief valve
- On compressor
- Checking, refer Fig. 1
13 - Compressor
- Sanden SD7-V16
14 - A/C clutch -N25-*
- Clutch assembly can be serviced without discharging refrigerant system.
- Servicing.
15 - Receiver drier
Fig. 1 Pressure relief valve, checking
- Function: Protects refrigerant circuit from over-pressure.
- The pressure relief valve plug indicates if valve has opened to release pressure - arrow-. An adhesive plate is pushed out.
Fig. 2 A/C pressure switch -F129-, checking
Visual check: Ensure that O-ring (color: red) 10.8 mm x 1.8 mm 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 air flow over condensor 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
Checking switch function
- Bridge contacts -1- and -2- with engine running. If A/C clutch -N25- switches on, refrigerant system may be empty. Refer to "A/C Refrigerant System, Testing With Pressure Gauges" Testing and Inspection
Fig. 3 High pressure sensor -G65-, checking
Function
Where equipped, the high pressure sensor -G65- -B-, 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 -G65 is processed as follows:
Based on the pulse rate transmitted by -G65-, -J293- determines the A/C refrigerant system pressure and controls the function of the A/C clutch -N25- and coolant fan (s) accordingly. For example:
- Switches the radiator 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. Depending on the type of ECM, this signal may or may not appear as a duty cycle on the read measuring value block display (function 08).
High Pressure Sensor -G65-, Pin 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
Electrical checks
- Check voltage and ground supply to -G65- using wiring diagram.
- Check wiring for short to one another.
- Check wiring for short to B+ and ground.
- Check wiring for short circuit between -G65- and -J293- using wiring diagram.
- If no wiring faults can be determined, replace -G65-.
Fig. 4 A/C pressure switch -F129- and high pressure sensor -G65-, removing and installing
NOTE: Component can be removed without discharging refrigerant system.
- Disconnect electrical connection
- Remove switch/sensor -B-.
- Tightening torque 5 Nm (44 in. lb.)
- Replace O-ring seal -A- (10.8 mm; 1.8 mm)