MACS Monthly Newsletter - 2022 - JAN7

portant things to remember when temperature testing. 1.)
If a component has a total restriction, there will be no temperature
drop as you have to have refrigerant flow in order
to have a temperature drop. Also, a severe restriction
might not be detected by temperature testing, because
there is enough heat from the engine to offset what little
cooling is taking place with a very small flow of refrigerant
through the restriction. 2.) If you're temperature testing a
hose you must take the reading on the metal ends as the
rubber will act as an insulator and you might not be able
to detect a temperature drop through it. 3.) Last but not
least, you must use a contact type thermometer. Infrared
guns are just too inaccurate and will lead to the replacement
of parts unnecessarily. Can we go out into the shop
and do some temperature testing on it?
Him: Unfortunately, I have it completely apart where I
was blowing through those lines. But it does sound like I
need to put it back together and charge it back up and do
some temperature testing on it tomorrow.
Me: Yes, just be sure you get the correct charge in it. I
would come over tomorrow when you temperature test it
but, I'll be in a different city. I'll give you my phone number
so you can call and let me know how things are going.
During the middle of the afternoon on the following day,
he called and said he had it fixed. It was blowing 42° air
from the vents and the high side pressure was just over
200 and the low side was in the high 20s and the customer
had picked it up. I asked what he'd found and what he
did to fix it and he said he'd replaced the suction hose. He
went on to say that when he temperature tested it, there
was a difference of about 50° from one end to the other.
He thanked me and said he had never been so glad to
get a car out of the shop. I asked what he'd done with the
hose, and he said he'd thrown it in the trash can. I asked if
I could possibly have the hose and he said he'd dig it out
of the trash and set it aside for me. I went by and picked it
up a couple of days later and I've taken it with me to just
about every A/C clinic I've conducted since that time, and
it's been used extensively to illustrate the effects that a
restriction can have on pressure readings. See Figure 8.
Upon seeing the hose, the first thing I did was hold it
up to the light and look through it. As you can see in the
picture, it is only about 15 inches long and has straight
metal tubing on one end and only a slight bend on the
other end so it's very easy to look completely through it.
The customer had indicated earlier that he had blown air
through it and detected no restriction, and it was easy to
see why. Looking through it, plenty of daylight could be
seen at the other end. However, upon closer examination,
something just didn't look right. Instead of being perfectly
round all the way through on the inside, it had more of
an elliptical shape to it toward the middle. To investigate
further, the next step was to cut the hose apart. Once cut
apart, it was easy to see what had happened. It is a barrier
type hose and the inner liner had come loose as indicated
in the picture. See Figure 9.
So, what was actually going on here? There were several
inches of the internal liner that had come loose from
Figure 10: This illustration of the Honda A/C system shows the location of the service ports, location of the
restriction and the pressures at those ports with the restriction in place.
January 2022
7
MACS Service Reports
Richard Hawkins
MACS Monthly Newsletter - 2022

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