MACS Service Reports - 2015 - AUG8

Whether your customer's compressor uses a PID for
duty cycle or amperage for the DCV solenoid, there
should be a DTC if the solenoid is open / shorted electrically. Beyond DTCs and scan tool PIDs are three supplemental diagnostic methods.

Why take a chance of being wrong in my diagnosis and
end up having to replace the compressor later anyway?
2. What if they send me the wrong valve, and don't
have the right one after I've discovered the error? What
if I break something trying to replace the control valve /
solenoid?
However, a number of techs also go by this school of
thought. If the condition points to a control valve or solenoid, and if I can get the right replacement part at a
decent cost, and if I can change it out without removing
the compressor, I'll consider doing it. That's a lot of ifs as
variables in a repair decision, but variables are what it
sometimes takes to keep your customers cool and saving
gas at the same time! ■

1. Multi Meter
Connecting your DVOM to the solenoid and checking
its internal resistance is a first step. Most are around 10
ohms. Follow up that easy test with the meter leads back
probing both wires to the solenoid and meter set to DC
voltage or % duty cycle to see if the duty cycle changes
with both pressure conditions and temperature settings
at the HVAC controller. An inductive amp clamp can be
used to determine the current being consumed by the solenoid. This would be the same bit of info from your scan
tool and should increase from low to higher (less than
1 amp) as the temperature is dialed down. This is very
important when working on a vehicle that you only have
generic OBD II data coverage for on your scan tool.

2. Lab Scope

MACS Staff

A DSO (Digital Storage Oscilloscope) is an ideal method for detecting the square wave from the control unit
to the control solenoid. When you actually 'see' what is
coming out of the HVAC controls to the solenoids as the
temp controls are changed, you'll know if the problem is
the HVAC controller, the wiring or the solenoid.

3. Electronically Controlled Compressor
Solenoid Tester

Figure 13: GPD's ECCS06 system scanner can both display and command compressor duty cycle. It can also display the solenoid's ohm value.

MACS Staff

These testers vary in design, price and features. They
typically feature the ability to monitor the duty cycle signal from the HVAC controls to the compressor solenoid
and then control the solenoid manually while watching
your gauges to determine if the problem is mechanical or
electrical. Some will show you the solenoid's resistance
as well and include a package of factory pig tale connectors to place the tool in series with the various solenoids
you'll likely encounter in the field.

Real World Possibilities for Discussion
A large percentage of techs opt to just change the compressor out anytime something is wrong with them. If
the clutch is bad, it gets a new compressor. If the swash
plate is stuck or the control valve is faulty, replace the
compressor. The theory behind that is twofold.
1. It's difficult and expensive to replace the compressor.

Figure 14: Adiator's CLT1 can command compressor duty cycle, allowing
technicians to look for corresponding changes to manifold gauge readings.

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 Casey
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.

August 2015

MACS Service Reports

http://www.macsw.org

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