a 2010 models Tiggo SUV, equipped with SQR481FC engine, matching QR523 type manual transmission, mileage to 7 676 km, users reflect the car without air conditioning when cold.
After receiving the vehicle, the air conditioning compressor checked that the electromagnetic clutch can not pull. Generally reasons, causing the air conditioning compressor does not pull comprises: an air conditioning system refrigerant shortage, leading to low pressure cooling system is not working; A / C switch is damaged, it can not result in the output request signal conditioning; low voltage damage that can not the engine control unit provides the correct pressure signal; air conditioning compressor control relay burned fuse F4; failure due to other elements, causing the engine start control unit does not allow conditioning; short circuit, open circuit and virtual access lines related phenomena.
According to the above idea, the author observed the first dashboard. When normal engine operation, EPC indicator light on the instrument panel does not light up, indicating normal temperature, so initially ruled out due to engine control unit controls the strategy leading to the air conditioning compressor not working properly. Thereafter, the blower is turned on the author, press A / C switch, A / C switch corresponding to green light can be lit, indicating that A / C switch is working properly, also proved a good air conditioner control relay fuse work (A / C switch and air conditioning shared control relay fuses F4). Then they use into the engine control failure diagnostic system dynamic data flow was observed and found open A / C switch request signal and no air conditioning, or there is no refrigerant circuit phenomenon via the low pressure switch request signal line within the system? Because the car was traveling 7 676 km, without any incident, it is not considered a refrigerant leak. Use a multimeter to detect low voltage air-conditioning, low voltage switch found there is only 3 feet # 12 V voltage. Theoretically signal # 3 F4 fuse leading through the high-voltage power switch, the foot is over 1 # A / C switch signal over low-voltage power supply. At this time, no power pin # 1, indicating that the switch from the A / C out conditioned air conditioning request signal does not reach the low-voltage switch and, this switch can only be explained from A / C to low pressure air-conditioning switch between virtual connection or disconnection phenomenon .
FIG 1
After checking the correlation circuitryFIG. (FIG. 1) that, after a request signal from the air conditioner A / C switch # 5 feet premenstrual A / E goes directly to the low voltage connector pin # 1. A column ldquo found at the left front; front Ardquo; connectors, jacks examination E, where there is no result of 12 V voltage. Is switch from A / C to A connector for open circuit phenomenon before this line? But the car in addition to the installation of a DVD and paving glue, but did not do the other line changes. Related DVD carefully check modified line, found in the air conditioner blower 4 has a connector pin blank (FIG. 2). Is this due to connector off? Via the connector portion may be connected to the repeated examination, and did not find a corresponding 4-pin connector plug. Try holding the attitude, I checked the 4-pin terminal connector with the test light. On examination, it is found that a white line of the air conditioner A connected to the / C switch. When the A / C switch is closed, this terminal has power, after power is lost. Combined with previous maintenance experience, I believe that the connector should be connected to the indoor temperature sensor, but in the vicinity of the connector and no indoor temperature sensor.
FIG. 2
Thus, troubleshooting stalled. In order to be able to be found, I decided to look for a goods vehicle were compared to determine if the connector is empty or has been connected to the indoor temperature sensor. After comparing and goods vehicles, it became clear the fault. An original This connector has a short circuit (Figure 3), 4-pin connector of the white and red wires short-circuited. Directly with a line across the respective terminals 2, press again A / C switch, the normal operation of the air conditioning compressor, and a good cooling effect.
Figure 3
After a short circuit recovers, failure to completely eliminate.
Figure 4
Summary: By comparison a variety of similar models, I found that the car actually installed in 2009 on the indoor evaporator electronic temperature controller (FIG. 4), and the needle 4 is inserted in the connector on the controller. 2010 models Tiggo canceled the controller, in order not to change the wiring harness to reduce production costs, the 4-pin connector into a crowbar.Since the short-circuit in the installation DVD navigation and plastic flooring is inadvertently knocked maintenance personnel, resulting in A / C switch does not reach the low voltage signal. In this case, the engine control unit can not receive the request signal conditioning, naturally, does not control the air conditioning compressor. Troubleshooting this took some time, mainly model configuration changes while the corresponding maintenance information not kept pace.
(Qin Zhigang)