Porsche: Air Conditioning Black Death
Black Death encompasses the progressive failure of an air conditioning compressor due to any number of mechanical variables. Ultimately, and whatever the cause, a compressor suffering Black Death will be wearing itself out internally and so shedding particles of metal into the system’s refrigerant. Doing so turns refrigerant black in color---hence the moniker “Black Death.”
Were one to look only at the fluid from this compressor (below), its failure status would be clearly indicated by its' fluid’s color alone.
While it’s possible for a compressor to catastrophically fail and so immediately cease working, this compressor---from Porsche 911---experienced a slow death according to the wear seen within it. So severely worn are the pistons & cylinders that in the extreme, we can see one piston tilting over within its' cylinder. The metal that used to comprise these pistons & cylinders is now spread throughout this Porsche 911’s AC system essentially contaminating the ENTIRE SYSTEM. According to what's seen here, the cooling capability of this AC system experienced a slow, progressive warming to the point of providing no cooling capability at all. (Owner confirms this.)
Piston o-ring material is found logged in the reed mechanism. Since o-ring material does not typically escape a piston, some other failure led to these o-rings being where they do not belong.
A good reed seat followed by one that’s been deformed by o-ring material lodging between reed and seat.
This reed plate should be entirely flat.
It’s possible to flush a Black Death AC system, however, doing so is rarely attempted by professional Porsche shops for two reasons:
Time required is significant and…
After time was given to flushing, there’s NO GUARANTEE how well a system has been cleaned out---any residual contamination can translate into the system working poorly or in the worst case, yet another significant failure. You can see why flushing a Porsche system is not worth the time or risk.
Only by replacing certain components with new parts can there be a guarantee of lasting AC system performance. Provided the capability & equipment, some shops can and do flush certain kinds of Porsche AC hardware successfully.
FLUSHING PORSCHE HARDWARE
Tube & fin condensers and tube & fin evaporators and piccolo units can be flushed successfully---their internal passageways being sufficient in diameter to allow complete cleaning. Serpentine is borderline. Parallel flow components---because of their small diameter passageways---should not be flushed. If they are, it’s risky, ill advised business.
Below, the case study 911’s rear lid tube & fin condenser has just been blown out. Glittering specs in the discharge are bits of the compressor’s pistons and cylinder walls.
System’s hose cut in half. Interior walls are coated with a blend of micron metal particles encapsulated in the system’s mix of refrigerant & oil. This view illustrates the risk involved when attempting to flush 40 feet of contaminated Porsche 911 hose---it’s simply not worth doing. Again, the bottom line is one cannot have a guarantee concerning how clean any section of flushed hose is.
COURSE OF ACTION TAKEN IN THIS PORSCHE'S CASE
New parts purchased:
Receiver / Drier
Rear wheel well condenser (parallel flow)
Thermal expansion valve (TXV)
All hose with fittings and o-rings
Recycled parts---all are tube & fin and are flushed till proven pristine:
Rear lid condenser
Parts are installed then evacuated according to procedure. The goal being to:
Confirm the system being leak-free (or not). If a system leaks, find leak(s) and fix
Given a leak-free system, apply a rigorous evacuation procedure to ensure moisture within the system being completely eradicated
Prior to charging the system with refrigerant, oil specifications---type and amount---are confirmed with the new compressor’s manufacturer. Since many manufacturers preload oil into their units, the new unit is drained in order to check the quality and amount of oil present. Adjustments in oil volume will be made if necessary as manufacturer specs call for.
Compressor manufactures provide exact formulas from which the correct amount of oil for this Porsche---and any car---can be calculated.
The correct amount of oil to charge this particular Porsche's system is 6.5 fl ozs, almost exactly what was drained along with 0.5 fl ozs remaining in the compressor (according to manufacturer draining specs.) For a car with a shorter hose system, this amount of oil would have been too much.
Precision in regard to the amount of oil in an AC system is important. Too much oil insulates the system reducing the capacity of the refrigerant and hardware to perform optimally. Too little oil and the compressor will not be adequately lubricated. (Inadequate compressor lubrication is a cause for Black Death. Given the evidence in this case, there’s a possibility this compressor experienced oil starvation.)
Most Porsche owner’s are not aware of the fact that servicing their AC system can/does alter its oil content. This is because as refrigerant leaks or is removed from the system, oil goes with the refrigerant to some degree. Over time, multiple AC service events and/or a system leaking has a cumulative effect on the system’s oil volume. With this in mind… some tips for you:
1. Keep accurate track of every AC service noting who, what, where, when, and why. This record provides reference allowing an intelligent Porsche AC person to understand the systems history and most importantly… estimate the oil status of your system. While not an exact science, it’s better to have reference that allows an informed oil calculation to be made compared to having no idea at all as to how much oil your system has.
2. Because Porsche AC systems are intrinsically different than front engine cars, it’s best to go to a recognized Porsche maintenance specialist. Once there, qualify whomever may work on your Porsche’s AC system by asking a few questions that proves their expertise. If you’re not confident in the shop… best to respectfully exit and find someone you’re confident in.
CHARGING THE SYSTEM
We know a 3-condenser system as is in this Porsche 911 performs extremely well with 26 dry hose weighted ozs. of R134a. The system is weight-charged accordingly. Appropriate pressures are confirmed afterwards.
Black Death is clearly evident in this system---oil starvation is a possible cause
Correct decisions are made regarding what AC system parts to discard and what parts can successfully be recycled
Recycled hardware is flushed till proven pristine
New, quality replacement parts are bought
Proper installation & connections are made so system is proven leak-free---testing confirms leak-free status prior to moving forward
Compressor manufacturer’s oil specifications are followed precisely based on the particular Porsche system being worked on
Thorough evacuation of the system ensures comprehensive moisture eradication (moisture in an AC system degrades performance)
Optimal refrigerant charge is installed and system’s performance is confirmed.
Cabin’s vent temp was recorded after 15 minutes city driving in 87 degrees ambient with 62% relative humidity. Vent temp and pressures are at engine idle.
A consistent vent temp of just above 32 degrees F indicates this Porsche AC system operating at optimal performance. From the compressor cycling ON and OFF at regular intervals while maintaining a 33 dF vent temp, we know the capillary and thermostat are performing as they should (preventing the evaporator from freezing as would occur in a humid climate and were the evaporator to drop below 32 dF.)
If you’re not satisfied with the cool your AC is offering you… we can help. We’ll gladly make a cursory inspection and share our expertise with you---complimentary of course. Perhaps you can make the necessary adjustments yourself. If you want our help… that’s what we’re here for. Please schedule with us before coming by: (305) 588-0874
For more information on our comprehensive Porsche service and repair capabilities, we invite you to go through our website: www.GPAutowerks.com
Think to buckle up… because someone loves you!