7 things to consider when working with your Masterflux system

Mark recently made a post to the Electric Vehicle Discussion List (EVDL) about working with the Masterflux systems and I thought it had some good advice to potential installers. Here is the unedited post:

Auto AC is a tricky thing to do well. Few technicians today have the
skills to actually work with a custom system. R-134A is not as
forgiving as R-12 was, refrigerant charges and oil charges have to be
just right. Most technicians are fine with changing hoses and
recharging a system to factory spec, but they lack experience doing
the careful calibration of charge required.

Most common errors we see with the Masterflux units:

1. Not flushing the system to remove all of the factory PAG oil. The
motor in a Masterflux compressor is submerged in refrigerant and oil.
You MUST use only non-conductive PVE oil. The compressor comes
precharged with 10 ounces, which is enough for the compressor and most
normal sized AC loops. And yes, it MUST be done no matter what the
technician thinks.

2. Overcharging with oil. We used to sell 4 ounce bottles of oil to
add to the loop, to make up for the 1-3 ounces of oil that gets
trapped in various spots. We had too many installers dumping the full
bottle in. Oil isn’t compressible. Too much damages the compressor
and motor, and prevents refrigerant from flowing. We no longer
recommend make up oil.. the oil included in the compressor is enough
for most cars.

3. Too little/too much refrigerant. This is the hard one… you used
to be able to use the gauges to get a pretty good idea of the right
charge level. But R-134a varies significantly in pressure based on
the temps inside and outside the car. The Masterflux units are
slightly undersized so it can be hard to get the low side as low as
expected, and the high side as high especially on hot days. As
terrible as it is, I find the most accurate method is to watch the
suction line on the compressor. You want water to be condensing on it
close to the compressor, but not on the compressor body itself. The
larger compressor on the Masterflux unit stores a little more
refrigerant than most factory units. If you didn’t change the hoses
too much expect it will take about 4-8 ounces more refrigerant than

4. Insufficient condenser capacity. R-134a can’t be compressed and
compressed until it gives up heat. You need to get the heat out of
the refrigerant for it to condense. This means a modern parallel flow
condenser. We do not recommend reusing a R-12 condenser, and you must
ensure that the electric cooling fan is blowing over the condenser
whenever the system is engaged.

5. Failure to use the factory pressure switches to deactivate the
system. The overpressure and underpressure switches are not just
safety backups, they are actively used tor managing the system.
Running a system too low can damage the compressor from lack of oil,
to high can blow out seals or stall the compressor.

6. “Zilla” (or any controller) damage. The input capacitors on the
Masterflux controller are low ESR, hence under acceleration they can
look like a better electron source to the controller than the traction
battery. This usually manifests as AC controller shutdown under
acceleration, or blown input fuses on the AC controller. Masterflux
now recommends a series input diode in all vehicle installs. [for more details on this, please refer to the Masterflux Recommendations for Battery Powered Applications]

7. Insufficient cooling due to trapped air. Atmospheric air isn’t a
refrigerant. Many of us leave the system open to air for months
during conversion. (Don’t do that, keep the lines sealed and capped)
Pulling the system to vacuum is not enough to remove all of the
trapped air, even if the vacuum is held for a long time (we’ve tried
weeks, it doesn’t work). In our experience it usually requires one or
two charge, run for a brief time, recover/recycle and recharge cycles
to get best performance. Your AC technician will need a recovery and
recycling machine capable of separating air from refrigerant.

Most important, installing automotive AC is a difficult and
potentially hazardous operation. It is not a do it yourself project.
Specialty tools and know how is required. Even for skilled techs it
can be difficult to do correctly. If you are not getting expected
results, or the system appears to be making unusual noises or not
cooling as expected shut it down and contact support.

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