AC Low Side Pressure Too High? Common Reasons

Summer’s here and you just wanna chill. But when that old AC kicks on, nothing but lukewarm air comes out. Ugh. What gives?

Well friend, there’s a good chance the low side pressure is too high. And that can spell t-r-o-u-b-l-e for your cooling system.

But before we dive into why low side AC pressure gets whack, let me hip you to what it actually is real quick.

The low side pressure reading comes from the low pressure line between the evaporator and compressor. It measures the pressure and temperature of the refrigerant after it leaves the cold evaporator coils.

A higher than normal low side pressure means the refrigerant isn’t expanding and absorbing heat properly. Which is a problem, ya dig?

Now let’s break down a few common reasons your AC’s low side may be pressurized, and how to fix it:

Your AC’s Packed With Too Much Refrigerant

Also called an overcharge, too much refrigerant in the system makes it hard for the evaporator to fully absorb heat. And that pressure stacks up on the low side.

Some signs your AC’s got the overcharge blues:

• Low side pressure above 30 psi (the norm is under 30)
• Frost on the suction line like it’s a Minnesota winter up in there
• Bubbles in the sightglass
• weak airflow from the vents

The remedy here is to drain some of that excess refrigerant until you reach the proper levels. Your AC technician can handle that with some vacuuming magic.

The Condenser’s Clogged Up

When debris, leaves, and other gunk block the condenser coils, airflow suffers. That heat can’t escape like it should, leading to high pressure creeping down the line.

Watch for:

• The condenser fans cranked on high trying desperately to pull air
• Warm, not cool, air pumping from the vents
• Low side pressure over the norm

Bust out the hose and spray down the condenser to remove all that dirt buildup so air can flow free again.

Thermal Expansion Valve Is Jammed Up

This little component regulates the flow of refrigerant after it leaves the condenser. If it’s stuck shut or not opening properly, pressures spike.

Signs of a troubled TXV:

• Frost forming around the valve
• Bubbles in the sightglass
• High low side pressures

The remedy here is to replace the janky valve with a shiny new one so refrigerant flows like it should.

Airflow to the Evaporator is Blocked

Without ample airflow over the evaporator coils, the refrigerant can’t absorb heat and pressures start climbing.

Things that squash evaporator airflow include:

• Plugged air filter that needs swappin’
• Debris blocking the evaporator housing
• Blower fan issues
• Closed vents and registers

Inspect the pathways to the evaporator and remove any obstructions. Clean or replace that grimy filter too. A free flow of air helps keep the low side pressure chill.

When the low side pressure creeps up, your AC system can’t properly remove heat. Tackle problems early before they lead to bigger issues down the road. And remember – a certified AC technician has the skills to accurately diagnose and treat excessive low side pressure.

Our cooling systems work hard to keep us comfy during hot weather. But when we notice signs of trouble like weak airflow or higher than normal low side pressures, it’s time to take action with a checkup and repairs. With a properly operating AC unit, you’ll stay chill all summer long while keeping energy costs in check.