My AC Guy Says My Refrigerant Pressures Are Bad
Your AC guy connects gauges and says:
“Your pressures are bad.”
Okay.
What pressures?
And more importantly:
What do they tell us?
Because there isn’t one universal set of “good AC pressures.”
What Should My AC Pressures Be?
Depends.
Refrigerant pressures change with operating conditions.
Things like:
- refrigerant type
- indoor temperature
- outdoor temperature
- indoor humidity
- airflow
- equipment design
- system load
all affect what we expect to see.
So if somebody tells you:
“Your suction pressure should always be 120.”
We’re missing quite a bit of information.
A pressure that’s perfectly reasonable under one set of conditions may mean something completely different under another.
This Is Why We Measure Temperatures Too
Pressures become considerably more useful when we combine them with temperature measurements.
That’s how we calculate things like:
Superheat
and
subcooling.
Those measurements help us understand what’s actually happening with the refrigerant inside the system.
For example, unusual pressures could potentially point us toward:
- incorrect refrigerant charge
- airflow problems
- refrigerant restrictions
- metering-device problems
- condenser problems
- compressor problems
- other system conditions
Notice how that list contains considerably more than:
“Needs Freon.”
Low Pressure Doesn’t Automatically Mean Low Refrigerant
This is one of the big ones.
A low suction pressure can occur with an undercharged system.
But it can also occur with poor airflow or a restriction.
That’s why we don’t want to see one gauge reading and immediately start pouring refrigerant into the machine.
Likewise, high pressure doesn’t automatically mean:
“Too much refrigerant.”
Again:
What’s happening with the rest of the system?
What Should You Ask?
If your technician tells you the pressures aren’t right, ask:
“What were the pressures, and what other readings confirm what’s causing them?”
A good answer might include:
Superheat.
Subcooling.
Air temperatures.
Outdoor temperature.
Airflow.
Now we’re putting together a diagnosis.
The Klein Answer
Your refrigerant pressures can absolutely tell us something is wrong.
They’re an important diagnostic tool.
But:
Pressure is a measurement.
It isn’t automatically a diagnosis.
If your AC guy says the pressures are bad, he may be completely right.
We just need to finish the sentence:
“The pressures are abnormal, and these other measurements show us why.”
Because two gauges hanging off the side of your condenser aren’t a Magic 8 Ball.
We still have to interpret them.