MACS Monthly Newsletter - 2017 - APR8

The oil separator is a key part of the newer compressors, and its purpose is obvious: with today's lower oil
charges, the compressor gets effective lubrication by
keeping almost all of the oil in the compressor, not allowing it to flow out through the circuit with the refrigerant.
That also reduces the energy required to operate the compressor, as even droplets of oil take power to be circulated. It's not uncommon to see oil charges of four ounces
or less, and as an example, the Chevy Cruze oil fill (with
R-134a at this writing) is just two ounces.
Here's a look at the Denso unit in the Camry we've
been talking about. The oil and refrigerant flow into the
separator (FIG. 12) from the discharge chamber port into
the separator. The movement of the flow causes the oil
separator cylinder to turn, which produces centrifugal
force that separates the oil and refrigerant. The refrigerant flows to the condenser through the discharge port.
The oil flows through the reservoir chamber, into the inlet, cylinder and discharge chambers, lubricating the internal parts of the compressor in the process. This separator does make it difficult to drain oil from compressors of
this type, and because of the low charge, you should not
expect a lot to be removable, during refrigerant recovery
or when trying to remove oil to balance the charge prior
to compressor replacement. The draining issue will be
something you'll encounter on many new compressors
with oil separators, some more difficult than others. ■

techinfo.toyota.com

OIL SEPARATOR

Figure 12: Oil separator keeps most of the oil within the compressor, so oil change
can be minimized for maximum efficiency. Separator sends oil through reservoir
chamber, inlet chamber, cylinder and discharge chamber. Only refrigerant (and a
minimum amount of oil for circulation of any trace dye) flows with the refrigerant.

REFRIGERANT BLOWS OPEN THE PRESSURE RELIEF VALVE
"replaced everything," - the compressor (well it was leaking,
so...), condenser, orifice tube, radiator, fan clutch assembly and
the rear expansion valve. And when the throttle was blipped,
the technician could verify good airflow through the front cooling module. Yes, the technician also had flushed all the refrigerant lines and hoses, and even the evaporator. So what could he
have missed?
The answer: getting a full vehicle history, which would have
told him that a compressor previously had been installed. That
compressor failure had left debris wedged in the line to the condenser, and despite the maximum effort at flushing, it hadn't
budged. Use of a premium infrared thermometer should have
picked up the pressure drop to the condenser, instead of having
to go through a physical inspection with a rod. ■

When a pressure relief valve starts popping off, the problem
(refrigerant escape) should be reasonably straightforward to diagnose, right? The PRV is defective, something is causing the
high-side pressure to go way up, or there's a restriction. It becomes an issue when the technician can't seem to find the answer in one of these "obvious" possibilities.
The vehicle was a 2006 Ford E-450 outfitted as an ambulance
with the 6.0-liter Super Duty diesel. No, we're not going to find
something weird with the engine creating the problem. And although the long hoses in ambulances do create a leakage issue,
this case is a verified loss through the PRV.
The pressures started at 30 psi low side and 325 psi high side
at idle, and when the technician blipped the throttle, the high
side pressures went to 500 psi (low side drops to about 20 psi),
at which the PRV obvious would open. The shop already had
MACS Service Reports is published monthly by the Mobile Air Conditioning Society
Worldwide. It is distributed to members of MACS Worldwide and is intended for
the educational use of members of the automotive air conditioning service and
repair industry. Suggestions for articles will be considered for publication, however,
MACS Worldwide reserves the right to choose and edit all submissions.

Editors:
Elvis Hoffpauir, Steve Schaeber
Production Designer:
Laina Forcey
Manager of Service Training:
Steve Schaeber
Mobile Air Conditioning Society Worldwide
P.O. Box 88, Lansdale, PA 19446
Phone: (215) 631-7020 * Fax: (215) 631-7017
Email: membership@macsw.org * Website: www.macsw.org

Unless otherwise noted, all photos/art by author.

April 2017

MACS Service Reports

http://www.techinfo.toyota.com http://www.macsw.org

Table of Contents for the Digital Edition of MACS Monthly Newsletter - 2017