Fault phenomena
The owner of the 2005 volkswagen pasat autobus, carrying 1. 8t turbine booster engines, travelled 235,130 km, indicating that the auto-air conditioner of the vehicle pressed the auto key on the e87 air conditioning display and operating module, that the central vent was not cooled, and that the observation of the low speed of the electric fans was not activated and that the air conditioning system was not cooled。
Diagnosis and elimination of malfunctions
A connection to the vas50 52 malfunction diagnostic device, clicked on the ac control unit, j255 at 08, searched for the malfunction memory and found static failure code 00792: ac pressure switch f129. The reading of the measurement value 1 block 1 compressor closure condition of 3 means that system pressure is too low, consistent with reported failure code 00792, failure code 00792 in maintenance practice often means inadequate refrigerants in air conditioning systems, connections to chillers, pressure tables indicate a system pressure of 8. 0bar (1bar = 105 pa), indicating sufficient refrigerants and f129 or circuits。
Four needle plugs in f129 were checked, the brown/red line on the low-pressure switch was disconnected and the failure code 00792 was removed after repair of the circuit, but the system was still not refrigerated. Read again the measurements of the closure conditions of the compressors in group 1 sector 1 (figure 1) and at this time show 12, meaning that engine control unit j220 does not allow air conditioning。
Figure 1
Reasons for not allowing air conditioning work in the engine control unit include entry into engine control unit j220 to search for malfunction memory, finding failure code 16486: low-level input of mass or volume air flow, static. The measurement of air flow is 0. 5 g/s for group 2, block 4, the air conditioning switch is low for group 50, group 3, block (1. 8t vehicle, regardless of whether the air conditioner switch or off is always low), and the compressor is closed for sector 4. The measurement of the endpoints on the g70 plug, the presence of the 12v voltage from the fuel pump relay j17, the normality of the power supply of the 5v sensor from j220 output indicates that the maf is in trouble, and that if the g70 is damaged, j220 cannot accurately calculate the load, at which point air conditioning will not be allowed。
The maf was replaced to read the measurement value of 2 group 4 sectors 2. 7g/s, and the compressor of 50 group 4 was activated and the engine control unit allowed air conditioning. Read again the j255 data block, and the number of the number of the closures of the compressor in block 1 becomes zero, normal. The observation of electric fans is operating at a low speed, but the central vent is still hot, the system is still not cool and the failure appears to have not been resolved。
According to the pasat ac circuit map, the electrical level of the 4/86 endpoint of j44 was 1. 2 v, measured on a single scale, indicating that j255 had exported the ground control signal, that, in normal times, the electromagnetic wire should be powered to close the frequent contact, remove the t1h green plug on the side of the abs pump, and measure with a 12-v test light, which did not light, indicating that j44 did not export power to n25. The suspicion is concentrated on the ac relay j44 (267)。
There are still a number of possibilities at this time, such as belt skimming, poor power supply to compressor relays, poor operation of compressor clutches, inefficiency of compressors and inadequate refrigerant filling. Of course, first-inspection relays are also feasible, based on the principles of easy-to-facilities, simplicity and complexity。
A single-body test of j44 was performed, as illustrated in figure 2. The electro-magnetic wire loop resistance (between 85 and 86 enders) measured by the meter was 98 times, the electromagnetic wire circle was added to the 12v voltage, and the vibration of the contact was felt by the hand, at which point the directed relays were measured at 30 and 87 enders, the electro-retardation value was 4. 7 times as shown by the meter, the electro-magnetic circle n25 of the compressor was 4. 5 times, and the voltage distribution on the omnibus line would be less than 6 v on the n25, so n25 could not absorb the work。
Figure 2
An air conditioner relay, j44(267), was subsequently replaced, and as shown in figure 3, compressors were inhaled and non-refrigerated air conditioners were completely eliminated。
Figure 3 location of pasat air-conditioning relays
Maintenance summaries
In general, it is not sufficient to judge whether the volume of refrigerants in the tube is sufficient to detect staticly the pressure in the high-pressure pipe, since the pressure of refrigerants in saturated states can vary with temperature. So we also have to test the dynamic pressures in the high-pressure tube to determine whether the coolant in the tube is adequate. In this case, the signal value on the pressure switch could be compared with the static measurement pressure, leading to an abnormal transmission of the signal on f129 rather than insufficient refrigerant charge。
The case is one of control failure, skilled handling of diagnostics, reading of the data block of the compressor closure conditions, and knowledge of the meaning of the compressor closure data are key to achieving a breakthrough. Knowledge and mastery of the upstream and downstream direction of electrical circuits and the definition of electrical endpoints are measured using a universal scale based on the principle of control in order to determine the point of failure. On the basis of the information obtained from the basic examination of the failure phenomenon, it was determined that the approximate extent of the failure was whether the failure was controlled or whether the air conditioning itself was mechanical。
This was a combined failure at three points: a brown/red line break in pressure switch f129 of an air conditioner, resulting in a storage failure code 00792 (air conditioner pressure switch), a data stream indicating low refrigerant pressure, and an air conditioner control unit j255 restricted the electromagnetic ion unit n25 sorption; 2 air flow meter g70 output values deviated from the true value, resulting in the engine control unit j220 limiting the electromagnetic ion unit n25; and 3 magnetic ionist relay j44 had poor contact with the contact point, resulting in a low electromagnetic ion n25 voltage。
A search of the circuit map, the t4bi plug-in for f129 (figure 4), with one needle of 15 electricity, two needles of pressure signal to j225, three needles of heat-dispersed fan high-speed signal and four needles of ground. The text states that the brown/red line of f129 should have been broken by a two-pile line, but that the circuit chart is a brown/blue line followed by a black/red line. An illustration of j44's needle-foot functions will allow readers to read clearly (figure 5), 2 or 6 are 15 electric, 4 are controlled by j255 and 8 are supplied to the n25 positive pole。
Figure 4 f129
Figure 5 j44
Clients call for air conditioners, first to observe whether the dashboard has a warning light to alert and then to check if the control units have a failure code, which will lead to early detection of engine control system malfunctions。
