Addressing the fact turbocharged engines are the new normal and introduce extra plumbing and heat exchangers into the engine compartment, the latest MACS bulletin discusses how easy it is to damage these components when attempting to access parts of the HVAC system.
Still on the subject of access, MACS also covers the difficulty of reaching, removing and reinstalling evaporators in modern vehicles. It can be heartbreaking if the diagnosis of a leaky evap turns out to be incorrect. Evaporator removal can now be a day-long job, forcing many technicians to develop shortcuts. MACS discusses the methods and potential pitfalls.
An interesting tip regarding evaporators is also included, but this is unlikely to hit Australasian workshops until the Holden Acadia arrives in local showrooms. According to the MACS bulletin, as the blower fan for rear passengers wears in from new, copper shavings from the motor brushes are picked up in the air stream and land on the evaporator for the rear cabin, causing a reaction between the two metals that leads to corrosion and a leak. To prevent it happening again, replace the evap but not the blower, otherwise it will happen again!
The bulletin also reminds readers they need to be able to reflash modules on modern vehicles, providing the example of a Chevy (Holden) Malibu and other GM products in which seat-heater wiring has become worn and shorted against the seat frame and produced an odd, intermittent symptom affecting dashboard and audio system displays. The solution is more complex than a case of finding and fixing the damaged wiring.
Of interest to our Toyota-saturated market is a piece about Denso compressors with in-built flow sensors. If the sensor fails, it is time for a new compressor. Information about diagnosis of flow sensor faults on these compressors is included in the MACS bulletin.
Still on the subject of compressors, MACS also goes into the presence of oil separators in modern pumps that enable smaller oil charges by keeping the majority of lubricant inside the compressor, rather than it flowing around with the refrigerant. Systems of this type will not yield much oil during refrigerant recovery and it is also hard to get oil out of the compressor once it is removed.
Finally, a case study about pressure relief valves and the importance of knowing what work had been previously done on a vehicle when attempting to diagnose HVAC faults.
This bulletin is highly recommended reading.
VASA members have exclusive access to MACS technical papers here.