Mercedes-Benz S350 air conditioner is not normal.
According to the above control principle, check the fan controller circuit first, because the electromagnetic clutch is directly powered by it. However, according to the driver, the car has changed the 1 new controller, so other switch signals should be abnormal. When the air-conditioning pressure combination switch is unplugged, the air-conditioning electromagnetic clutch stops working. According to the schematic diagram, it can be seen that the high-voltage switching power supply is powered by the ignition switch. If the high-voltage switch is turned on normally, the fan controller of the air-conditioning system will recognize that the air-conditioning system is in a normal high-voltage state at this time, so the cooling fan and compressor will be turned on. Check the switch with a multimeter, and the result is always on.
Troubleshooting after replacing 1 new pressure switch.
Fault 2: a time superman car, the air conditioning compressor stops working after half a minute, but starts working immediately, stops working after half a minute, and so on.
At first, the author thought it was caused by the system pressure, but it is normal to measure the system pressure with a pressure gauge. Because the system pressure is normal, the problem should appear in the control circuit or components.
For inspection, start the engine and turn on the air conditioner switch. At this time, the electromagnetic clutch of the air conditioner is repeatedly engaged and disengaged, but the cooling fan has been operating normally. It can be seen from the flow chart (Figure 2) that if the blower and cooling fan can work normally, the fault should be in the circuit below the outdoor temperature switch. In order to find the fault point quickly, the author decided to test the working performance of the switch in the engine room with the electric probe first. Firstly, the lead between the fan controller and the electromagnetic clutch is tested with an electric probe, and the electric probe flashes, indicating that the fault is in the related circuit above the fan controller. Then check the middle part from the outdoor temperature switch to the fan controller and turn off the air conditioning pressure combination switch. At this time, the electromagnetic clutch stops attracting, and the low-voltage terminal circuit of the pressure combination switch is tested with an electric probe. One end is always open and the other end is not open. When the air conditioning switch is turned off, the normally open end will also be cut off. The problem should be the wiring or electrical components between the low voltage switch of the air conditioning pressure combination switch and the air conditioning cut-off relay or fan controller. Plug in the pressure combination switch, turn on the A/C switch, test the line between the pressure combination switch and the air-conditioning cut-off relay with the electric probe, which is always on, and test the line between the air-conditioning cut-off relay and the fan controller with the electric probe, and the electric probe flashes. At this time, it can be determined that the fault range is the circuit breaker itself and the circuit, and the circuit is generally not problematic, so first remove the circuit breaker for replacement testing and troubleshooting.
When the circuit breaker is closed, it is found that the contacts have been severely ablated and the contact surface is very small, but what causes the excessive current between the contacts? Upon inquiry, the user learned that the air-conditioning compressor had just been replaced some time ago, because the bearing was "locked" and the fuse of the air-conditioning compressor in the fuse box was also damaged.
At this point, the reason for the failure is clear. After replacing the air conditioner compressor and fuse, although the system can work normally at that time, the electromagnetic clutch will definitely slip and the coil current will be too large because the compressor is not locked in time. When the air conditioner cut off the relay, the contact was seriously damaged due to the excessive current last time. After a period of time, due to the increase of temperature and resistance, the connected part was cut off. However, after the power failure, the temperature drop resistance drop circuit was switched on again, resulting in the above failure.