ACtion Magazine - July/August 2017 - 16

By Mike Bailey, MACS Heavy Duty Contributor

t's been said that cleanliness is next to godliness.
This can also be considered gospel when servicing
heavy duty (HD) and over-the-road (OTR) refrigeration. These systems operate in far more severe
conditions compared to those installed in the lowly
light-duty vehicle. All systems must be kept clean both
inside and outside, which is a tall order for HD and OTR.
Take a moment to consider the annual cycle of an OTR
system. It can sit for months in sub-zero weather and may
be placed into 24-7 service when seasons change. Consider what happens to the system during its down time.
While not operating, could the refrigerant leak out over
time? If not leaking, could undesirables enter the system
while idle?
Highway tractors also experience severe operating conditions, as many travel great distances across the continent. These systems may operate in severe southern heat
and humidity one day then head into extreme cold a few
days later.
Challenging operating conditions require that we technicians recommend the proper services for systems to
remain trouble-free when operators depend on them the
most. We must perform these services to the best of our
ability, avoid shortcuts and sometimes even take longer to
ensure the best job possible.
Shop equipment is another consideration. We are all
heavily invested in the tools and equipment necessary to
do our job. Equipment maintenance is important for its
longevity and extending service life. One benefit in maintaining certain equipment is improved performance, resulting in repairs of higher quality.

Vacuum
Let's talk about vacuum. Vacuum pumps need oil -
clean, uncontaminated, dry oil at the correct level. I make
a point of polling the audience during my training classes,
asking outright when the shop vacuum pump last got some

ACTION * July/August 2017

love. Here are some common responses:
* We change our pump oil every spring.
* Our machine tells us to change the oil, but
we just reset it and move on.
* We top it off every time we blow the oil out
accidentally.
* Vacuum pump oil can be changed?
* Vacuum pump oil needs to be changed?
* I put a gauge on every so often and it pulls
to 30 inches, so it's fine.
Changing vacuum pump oil is a simple operation that
does not require much time. But why do we need to change
the oil? It probably looks clean compared to engine oil,
but looks aren't everything and contamination can result
in a less than perfect service procedure.
After oil balancing, evacuation is one of the most important operations of our services. To understand why, it
helps to understand vacuum. There's a lot more to it than
just removing air.
First, let's consider atmospheric pressure at sea level - 14.7 PSI (pounds per square inch). What does that
mean exactly? It means that if we took a square sample
of air from sea level and brought it straight up into space
(approximately 600 miles) and weighed it, that column of
air would weigh 14.7 pounds. Atmospheric pressure applied to water determines its boiling point. At 14.7 PSI,
water boils at 212°F (100°C). The ultimate purpose of
a vacuum pump and the reason we evacuate a system is
to remove both air (a non-condensable gas) and (in some
cases) moisture. The deeper the vacuum we "pull" on a
system, the less air inside. The "deeper" the vacuum your
pump can achieve, the better the job it will do. This process takes time.
How deep can your vacuum pump "pull down"? When
we evacuate a system, we typically use a gauge set and
a separate vacuum pump (or RRR machine) with analog
gauges. Theoretically "perfect" vacuum is generally ac-

Table of Contents for the Digital Edition of ACtion Magazine - July/August 2017