Car AC Isn’t Cold: 3 Most Common Reasons and Solutions

Why Your Car’s AC Isn’t Cold: The 3 Most Common Causes and Solutions

It’s hotter than heck outside, and your car’s AC isn’t cold. You’d like to fix the problem yourself to avoid spending big bucks at the shop, but you don’t know where to start. This article will help you understand the most common causes and some tips on how to fix the problem yourself. Here’s a detailed guide to the most common reasons why your car’s AC isn’t cold, helping you diagnose and potentially fix the problem.

#1 Your Car’s AC isn’t cold because it’s low on refrigerant, there’s air in the system or both

One of the most common reasons your car’s AC isn’t cold is because it’s low on refrigerant. Refrigerant, often referred to as Freon, is a crucial component of the AC system that absorbs heat from the cabin and moves it outside the vehicle. If your AC system is low on refrigerant, it can’t absorb enough heat from the cabin to cool you down.

Car AC systems don’t use up refrigerant

Unlike an engine that burns oil that has to be replenished, AC systems don’t burn or use up refrigerant. If your car’s AC system is low on refrigerant, it has a leak. Understanding that crucial point is critical to getting the cool back into the cabin and keeping your AC working for a long time. In other words, if you add refrigerant to a leaking system, I guarantee you will have far more serious problems.

Where car AC systems typically leak refrigerant

• O-rings and gaskets— The refrigerant connections in your car rely on O-rings and gaskets. Over time, the O-rings and gaskets shrink, harden, and leak
• Corrosion on the condenser and evaporator— The condenser sits right behind the grille, exposing it to water, road salt, sand, and rocks. Over time, corrosion sets in, causing the condenser to leak. The evaporator, on the other hand, is constantly wet from condensation. As the water sits in the fins, it can cause corrosion and leaks.
• AC lines—Most car AC lines consist of aluminum tubing and rubber sections. The manufacturer uses a crimp connector to connect the rubber to the aluminum tubing. Over time, the rubber can shrink, and the crimp connection can leak.
• Compressor seals—The compressor is assembled in sections, each sealed with a gasket that can leak over time. The spinning compressor shaft seal can also wear and leak, especially if the system has accumulated debris.

If you don’t fix the leak, you’ll invite more problems

The leaks allow the refrigerant and refrigerant oil to escape. Worse yet, a leak also allows air and moisture into the system. Here’s what air does to your AC system:

• A car AC with 2% or more air will not cool properly, no matter how much refrigerant you add
• For every 1% of air in the system, you lose 1°F of cooling efficiency.
• When you reach 6% air, the system will stop cooling and possibly cause the evaporator to freeze up.
• If you don’t purge the air hose on your DIY recharge kit before you connect to the charging port, you will be adding air to the system (the air that was in the hose before you squeezed the trigger).

Here’s what moisture does to your car’s AC system.

• Moisture mixes with the refrigerant oil to form sludge that clogs the orifice tube and expansion valve.
• It reacts with the refrigerant to form acids that corrode internal components, causing accelerated wear.
• It freezes in the expansion devices, reducing cooling efficiency.

How to find and fix the leak

• Rent an electronic leak detector— Some auto parts store rent electric leak detectors, called “sniffers.” Run the detector around all connections to find the leak
• Use dye and black light— Inject dye into the system. Runt he AC for a few weeks and then use a UV or black light to find the leak.
• Pay a shop to evacuate the system. Then fix the leak, pay a shop to evacuate it again, and recharge it by weight, not pressure.

#2 Your Car’s AC Won’t cool because the compressor isn’t working

The compressor is responsible for pressurizing the refrigerant and keeping it circulating. A faulty compressor can significantly impact the cooling efficiency of the system.

• The compressor is worn out— A worn compressor can’t reach the pressures needed to cool properly.
• You have a faulty compressor clutch, flow control valve, or thermal fuse— These electrical components allow the compressor to spin, control the flow of refrigerant, and protect it from failure. If any of these components aren’t working, your car’s AC won’t cool.

Diagnose and fix AC compressor issues

The diagnostic procedures vary by year, make, and model. Get a shop manual for your vehicle and follow the testing procedures to identify and fix compressor problems.

recharge it by weight, not pressure.

#3 Your Car’s AC Won’t cool because the expansion devices are clogged, frozen or faulty.

An AC expansion device, either an orifice tube or a thermal expansion valve, is what meters high pressure liquid refrigerant into the evaporator inside the cabin. If it’s clogged, faulty or your refrigerant contains moisture, it can’t properly meter refrigerant and you won’t get cooling.

• The orifice tube filter screen is clogged—This is a common problem on car AC systems that leak, and the owner has repeatedly refilled it with a DIY kit. The moisture in the system combines with the oil to form sludge and debris that clogs the filter screen on the orifice tube. See the image below.

New and clogged AC orifice tube. Clogged tube shows evidence of “Black Death.”

Symptoms of a clogged orifice tube

• The AC cools immediately and then stops cooling—The debris caught in the orifice tube screen falls off the screen, allowing refrigerant to flow. As refrigerant pressure builds, the debris gets pushed back onto the screen, clogging it and preventing refrigerant flow.

• You get a bit of cooling but never enough to keep you cool— The flow is so restricted that the AC can’t keep up with cooling the cabin.

• The expansion valve isn’t working— The expansion valve can fail due to clogging or mechanical failure.

A block-style expansion valve meters the flow of refrigerant through the evaporator by varying the size of the orifice on the OUTLET side of the evaporator. It works by sensing the temperature and pressure of the exiting gas and moves a tapered needle/rod in or out of a small opening.

Clogged expansion valve

A capillary-style expansion valve meters the flow of liquid refrigerant into the evaporator the same way, but the valve is located on the evaporator inlet and uses a remotely mounted sensing bulb connected to the evaporator outlet tube.

How an expansion valve fails:

•The Sensing bulb loses its charge— Once that happens, the tapered metering rod won’t move and won’t allow refrigerant into the evaporator.
• The metering orifice gets restricted/plugged— Debris, leak sealer, deteriorating hose debris, sludge or metal particles and clog the small passages.
• Sticking due to wear—  Unlike an orifice tube system, an expansion valve has moving parts that can wear and stick.

Symptoms of a failed expansion valve

• No cooling or too little cooling— clogged orifice or stuck tapered rod
• The compressor clutch engages and immediately disengages— The pressure builds rapidly, and the high-pressure switch immediately disengages the AC compressor clutch.
• The low-side pressures are too low, and the high-side pressures are too high.

©, 2017 Rick Muscoplat