MACS Service Reports - 2015 - MAY6

Paul Weissler

For the earlier variable displacement compressors
with the mechanical control valve in the compressor,
it came down to either-or diagnostics, with debris contamination the most common issue. The compressor
was not seized, it seemed to be operating and the diagnostic approach, as noted by Jim Resutek, former
global service manager for Delphi, "replace the control valve and if that didn't work, replace the compressor." The control valve was often the issue and a new
one, easily installed, solved the problem. Of course,
sometimes it didn't. If there is a suction side screen
on the system, that may protect the valve (although
the screen isn't perfect). General Motors installed the
suction screen, but we've never heard of them (unless
installed after compressor replacement) with Sanden
compressors. And if a Sanden control valve fails, it's
not the easy replacement that it is on the GM Delphi
V5 and V7 compressors. In those cases where the valve
fails (with resultant no cooling), the compressor gets
changed.
The GM diagnostic approach is a performance test
with a graph that has boxed areas, and if the high and
low side pressures are both in the same box (zone), the
compressor apparently is destroked and you change

Steve Schaeber

Figure 6: CLT1 is a basic compressor solenoid valve tester. It sends duty
cycle commands to the solenoid and if it responds, the technician will see the
A/C pressures change in response.

Figure 7: The ECCS06 from Global Parts Distributors also can send
duty cycle commands to the compressor solenoid, but it also has plug-in
wiring harnesses to cover many compressor models (and a universal
harness for those applications not included in the kit). With the harness,
the tester can check to see if there is a valid command signal from the
vehicle's HVAC module to the solenoid.

Figure 8: GM diagnostic chart for the V5 compressor at 80°F. If both lowside and high-side pressures intersect in the D zone, that indicates the
compressor is destroked. Could be a completely failed compressor or just a
bad control valve; a replaceable part.

the control valve (Figure 8). As Resutek puts it, if that
doesn't work, change the compressor. Fortunately that
control valve is a very easy R&R.
By the way, as Resutek points out the control valve
for the V7 (a seven cylinder compressor used on some
systems for greater performance) is different from the
one for the V5. There were more V5s produced, so your
parts supplier (or the dealer if in the remote chance
he even stocks a detail part like that), might have
only the V5 valves. Don't use it on a V7 system. ■

Global Parts Distributors unit also can test the circuit from the control module up to the solenoid, so
you know if it's the problem area. But the bottom
line, of course, is that you can't just change out the
control module, because the problem could well be
in any of the sensor inputs for all those temperature
readings that the module uses to determine how far
to duty-cycle the solenoid. In fact, one of those sensors is more likely to be the problem.

May 2015

MACS Service Reports

Table of Contents for the Digital Edition of MACS Service Reports - 2015