MACS Monthly Newsletter - 2020 - AUG8

MAYBE THE "EASY" WAY ISN'T

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On a number of vehicles with a defective evaporator temperature sensor, to install a new sensor, the HVAC case has to be removed to replace the failed sensor. So, when the car maker gives
you an alternative that enables sensor replacement without having to pull the case, most technicians would breathe a sigh of
relief. After all, often among the preliminaries for removing the
case on a late model (or even not so late a model), will be pulling
the dashboard, lowering the steering column and removing the
airbag module. It's typically a full-day job or more.
The 2012 Chevy Silverado with Automatic Temperature Control fits into the "we have an alternative" category. The A/C was
inoperative, but the compressor could be turned on with a scan
tool. And the technician got a trouble code of B3933-05, which is
for an open circuit (or short to battery-unlikely) in the evaporator temperature sensor circuit. In addition, there was a scan
tool PID (data item) reading of -40°F for the sensor, a pretty solid
indicator of an open in the sensor circuit.
So, with a defective sensor pretty well assured, what's the
factory-recommended alternative that eliminates pulling the
HVAC case? Well, you first will want to double-check by disconnecting the sensor connector and plugging in a new sensor
to double-check the diagnosis of a bad sensor. That's good practice and in short order the technician confirms the Silverado's
sensor itself is defective.
Now for the matter of replacing it. The one used for the manual A/C model required pulling the HVAC case (Figure 11). The
one in the 2010-on model with ATC offered the opportunity for
replacement without as much invasive work. There was, however, more than one case being supplied, likely by different suppliers, and as a result, different service techniques. If you were
lucky enough to find a case with a rubber plug, you could remove the plug for access, but even in this instance, only after

Figure 12: This 2012 Chevy Silverado HVAC case for Automatic Temperature Control models (and others with ATC
from 2010 through 2013) had a factory work-around to avoid
pulling the dashboard and case to replace the evaporator temperature sensor. However, the airbag module and some other
under-dash parts did require removal, and a carefully located
hole had to be made with a hole saw, after positioning a service bulletin template.
removing the instrument panel compartment door, the airbag
module, the panel module, and the right side panel insulator
padding. If the HVAC case has that rubber plug, take it out and
you'll have access to the sensor.
More likely, there won't be the access plug, in which case
you'll have to drill a 1-1/4-inch diameter hole (using a hole saw)
in the right place (which you'll have to mark with a template
you can print out from the GM service bulletin). There are two
different templates, and the right one for the specific HVAC case
depends on a part number on the case (Figure 12). You have to
print out the bulletin to exact size, then resize it per dimensions
in the bulletin, cut it along printed ribs and tape it to the case (it
should fit snugly between the case's molded ribs at the bottom
of the case. You have to be really careful, because if you tape the
template in the wrong place and drill through the case less than
carefully with the hole saw, you might damage the evaporator
or the temperature flap door. We're not going to repeat the procedure in the bulletin-it's in your service information system. It
should save you hours versus pulling the evaporator case.
Don't be afraid. This job has been done by many technicians
over the years, very successfully, and it applies to a lot of 20102013 Silverados. And yes, GM parts department should be able
to supply a plug (No. 94535734) to seal that hole (coating its perimeter with silicone sealer). n

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Figure 11: Manual A/C Chevy
Silverados
in
the 2010-2013
period required
removal of the
HVAC case, an
all-day job, to
gain access to
the
evaporator temperature
sensor.

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.

August 2020

MACS Service Reports

http://www.acdelcotds.com http://www.acdelcotds.com http://www.macsw.org

MACS Monthly Newsletter - 2020

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