MACS Service Reports - 2015 - JUN8

cally controlled vacuum solenoid valve that modulates vacuum to a diaphragm unit built into a liquid-filled mount, so you have to check the electrical
end, the vacuum feed and the liquid-filled section
of the mount (Figure 9).
The metallurgy and mounting of automobile components affects the frequency at which they may
produce noise. Auto engineers run all kinds of tests
to excite parts of the car to determine if they are
likely to produce noise. So although the A/C turned
on may be the origin for the noise, the source of the
noise may be anywhere in the general area.

For example, the higher density of R-1234yf resulted in a pulsation that produced a noticeable vibration/noise on the Cadillac ATS with the 2.0-liter
turbo, because the A/C compressor mount was located very close to an engine mount. And although
engine mounts are designed to absorb vibration, the
combination of extra vibration in a specific frequency, very close to the front mount, was a problem the
mount did not muffle. Either that mount will be redesigned or the compressor might be moved when
the vehicle is changed over to R-1234yf. ■

CLUTCH DOESN'T ENGAGE
The 2007 Honda Odyssey clutch didn't engage, and getting a good 12-volt feed to the clutch, the technician was
able to isolate the problem to a defective coil. Okay, he
replaced the clutch and set the gap to specifications. Or
did he?
He sure thought so, and showed the feeler gauge he
used to the shop owner: .038 inch. "What's the spec," the
shop owner asked? "It's .035 to .060," he replied. Okay,
then maybe it's a bad clutch hub, he thought. But before
the technician went so far as to replace the hub, the shop
owner thought, "Geez, that's an awfully big gap." So he
checked the spec himself, and found it actually was 0.35
to 0.60 mm. That's millimeters, not inches, and the conversion, if your feelers are calibrated in inches, is just .014 to
.024 inches. So the .038 inch at which he had set the gap
was much larger than the .024 inch maximum.
The conversion factor for millimeters to inches is to
multiply by .04, and we suggest you use a calculator.
It's easy to make mistakes with metric to what we call
"SAE Customary" or "English" units. We make them occasionally, but at least we don't use the wrong ones, which
would lead to even worse errors in most cases.
As we've reported in the past, technicians also incorrectly use the wrong conversions for:
* Ounces to grams: there are 28.4 grams in an ounce,
although many specifications are based on a rounding up
to 30 grams. So if the refrigerant charge spec is 450 grams,
that's equal to 15 oz. But your recycling machine may
permit you to enter the charge you want in grams, which
eliminates the chance for error.
* Pounds to ounces: you might think that a technician
should know there are 16 ounces in a pound, and deep

down, he probably does. But he may not be so good at
decimals and the under hood label may specify charge in
pounds, like 1.3 lb. That is NOT one pound, three ounces.
It's one pound and 3/10 of a pound, which is one pound,
five ounces, or 21 ounces total. With today's small charges
and tight tolerances, you could easily see a performance
drop if the charge is two ounces low to start. The typical
charge margin is 10%, so all you've got to spare are those
two ounces.
Torque wrench settings are typically listed with the
weight first, followed by the length, specifically poundsfeet or pounds-inch and Newton-meters. However, most
listings for torque wrenches have it backward when it
comes to SAE/Customary numbers, specifically footpounds and inch-pounds. But let's use the correct references.
* Pounds-feet to Newton-meters (lb. ft. to N-m): This
is a torque specification, and there's a 36% difference, so
multiply by 1.36 to convert to Newton-meters (100 lb. ft.
equals 136 N-m).
* Newton-meters to pounds-feet: If the spec is in Newton-meters, you have to multiply by 0.74 to convert to
pounds-feet (100 N-m equals 74 lb. ft.).
* Pounds-feet to pounds-inch (lb. ft. to lb. in.): If a spec
is in pounds-feet, with small torque settings, you may
have to go down to pounds-inch. There are 12 lb. in. per
lb. ft., so one lb. ft. equals 12 lb. in. Use a small torque
wrench calibrated in pounds-inch.
* Newton-meters to pounds-inch (N-m to lb. in.): Multiply by 8.85 to convert, so 10 N-m equals 88.5 lb. in. (although multiplying by 9 gets close enough at 90 lb. ft.). ■

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.

June 2015

MACS Service Reports

http://www.macsw.org

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