MACS Monthly Newsletter - 2022 - JAN6

later with the same results. There is another problem with
that system and it's going to be necessary to diagnose it
and fix it to ever get that system to cool properly.
Him: Well, what in the world could it be?
Me: Assuming that your charge is correct, most likely
a restriction. Also, an expansion valve that is stuck wide
open (which isn't all that common) can affect pressure
readings.
Him: I've replaced the expansion valve twice and that
didn't make any difference and it can't be a restriction because
that would cause the high side pressure to be too
high.
Me: Well with 3 different expansion valves and no difference,
we can almost surely rule out an expansion valve
issue. But a restriction isn't necessarily going to cause the
high side pressure to be too high.
Him: Why?
Me: It depends on where the restriction is and also
where the service ports are located in relation to the restriction.
For example, it's very common to have a severely
restricted expansion valve. It can happen because debris
might become lodged in it or because it loses its charge
and won't open. But when this occurs, the low side can go
into a vacuum and the high side might only be 100 to 110.
The reason the high side pressure is so low is because
once the low side goes into a vacuum, there is very little
refrigerant being pumped through the system. Also, most
of the refrigerant is residing in the high side between the
compressor and the expansion valve, where there is plenty
of room for it, and the airflow through the condenser is
keeping it pretty close to the temperature of that air.
Going a step further here, a restriction in the discharge
line could definitely result in some very elevated high side
pressure, but depending on the location of the high side
service port, you may or may not see it on your gauge. If
the service port is located between the compressor and
the restriction, the gauge would read high. If the service
port is between the restriction and the condenser, the
gauge will read lower than the pressure at the compressor.
Him:
So, you're saying I have a restricted discharge line?
Me: You could, if your service port was located after
the restriction, but a restricted suction line could cause
the same type readings as well as a restricted condenser
or drier, again depending on the location of the high side
service port.
Him: Well, we can rule out a restricted discharge line
or suction line and liquid line too for that matter. I took air
and flush and blew through all of them and they all flow
just fine. Also, I replaced the condenser so there shouldn't
be a problem with a new condenser.
Me: It's unlikely there is a problem with that new condenser,
but any of those lines could have a restriction in
them.
Him: How is that possible? I said I took air and flush and
blew through them.
Me: If you have a TOTALLY restricted line or SEVERLY
January 2022
6
Figure 9: Cutting the hose in two at about the midway
point revealed exactly what the problem was. The inner
liner had come loose from the adjacent layer it had been
attached to.
MACS Service Reports
restricted line, you could likely find it by blowing air or
flush through it. But it's possible for a hose to flow air or
flush just fine when you have it off the system, but when
you have it installed on the system and charge it up and
try to flow refrigerant it can become restricted due to a
problem with the internal liner.
Him: Wow. I hadn't thought about that. So how would
you find a restriction like that?
Me: By temperature testing. When you have a pressure
drop, you are going to have a temperature drop. You need
to check the temperature on the inlet and outlet of each
component that you're testing for a restriction. With the
exception of the compressor, condenser and the expansion
valve, there should be very little temperature difference
from inlet to outlet on any of the other components
in the system when it is operating. There are several imRichard
Hawkins
MACS Monthly Newsletter - 2022

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