MACS Service Reports - 2015 - OCT4

Why 95% as a Minimum Required Recovery Percentage

to perform certification test, with some margin for error. The
test is performed on a 3.0-lb. system in a Chevrolet Suburban, which research indicated was a readily available tough
case for the recovery standards. This orifice tube system has
an accumulator. The rapid deep vacuum which occurs with
some machines during refrigerant recovery can produce a
layer of chilled oil over the remaining refrigerant, making
further recovery difficult without a preventive time-out. The
recovery strategies of the different equipment manufacturers may use a number of timing variations to meet or exceed
the requirements of the SAE standards.
All this said, the recovery process is based on the equipment maker's confirmed algorithms, using system capacity
and ambient temperature. Single-evaporator, smaller-capacity systems, in our experience, may be finished with recovery in half the maximum amount of time on a hot day. In fact,
the last two systems we tested (one 28 oz capacity with 13 oz
removed, the other 36 oz capacity with 15 oz removed), on a
hot day completed the recovery phase in about 10 minutes.

The 95% refrigerant recovery requirement and ± one ounce
charge accuracy also were not pulled out of the air. EPA was
asking us to push the envelope for environmental reasons,
and we were looking at a percentage that would enhance
the value of buying and using the machines. At 95%, the
equipment would have to perform right in the middle of the
10% extra charge that was the historic amount in automotive
A/C. That would eliminate any excuse for a technician adding a few extra ounces just to be sure. Accuracy in recovery
and recharge were high priorities.
Some amount of time just short of the specified maximum
of 30 minutes turns out to be what virtually all equipment
makers have been using as time to recover for the toughest
systems; large, dual-evaporator systems, at low to moderate
ambient temperatures of 70-75°F. This is because equipment
manufacturers use computer-controlled strategies for the
process (which includes time-out, then resume for outgassing)
to be able to achieve the minimum 95% recovery required
by the standard. By using all (or virtually all) of the available
time, a manufacturer may exceed the 95%, which of course
would be an advertising point. Bosch/Robinair, for example,
was able to certify its latest R-134a machine, the No. 34788NI
and 34788NI-H (for high-voltage electric drive compressor
systems as used in hybrids and electric vehicles), to a reported 98.5% recovery. See Figure 6.
But more important, going to or close to the full 30 minutes ensures that the equipment passes the very expensive

Why All the Automation?

Robinair

There have been complaints that the machines are so automated, the technician can't override them to shorten the
cycles. Well, that's the idea, although there is some flexibility
in the air evacuation time. The cycles are there to meet the
SAE standards for performance, so you shouldn't be trying to shorten them beyond the evacuation default time for
air removal. Because they're automated, unless you choose
machines that also have manual operation, you don't have
to stand around pressing buttons or operating valves for almost all of the steps. In fact, Mahle/RTI has a wireless device
for your shirt pocket that can let you know when the job is
complete, so you can be working elsewhere in the shop in
the meantime.
The R-134a recovery step is what it is, based on system
capacity and ambient temperature, perhaps with an adjustment for type of system. Although an equipment maker
is free to shorten it from the specified maximum, it makes
more sense to use as much time as needed, up to the full 30
minutes, to raise the recovery percentage. The R-134a machines then require evacuation for air removal from the system. No specific time specified, just that the system is 98%
free of refrigerant and air prior to recharge. The air removal
perhaps may be recommended for up to 30-45 minutes, but
can be shortened to at least 5-15 minutes. The machine follows with an optional leak test to ensure the system holds a
deep vacuum for about two minutes, then goes into a quick
recharge with recycled refrigerant. If you wish to skip steps,
you can finish in under 40 minutes, and in our last two cases,
in just about 30 minutes.
The R-1234yf machines go through more steps and therefore may take somewhat longer. First, they must identify the
refrigerant, a feature added to prevent refrigerant cross-contamination. Yes, this can take a few minutes; maybe an extra
couple of minutes more if you're using a handheld identifier
and plugging it into the machine's USB port. Just a cautionary note: if you've replaced the filter or done other service

Figure 6: New R-134a machines will still get many years of future use. This
34788NI by Robinair claims 98.5% recovery efficiency.

October 2015

MACS Service Reports

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