Car AC lines freezing up? Here's what you can do about it

Helpful tips from Don’s Pro Tech Automotive


June 19, 2021

When summer’s here, or really any time you want cool, dry air while driving, your car’s air conditioner (AC) is critical to your comfort and safety. Unfortunately, frozen AC lines can put a major kink in your road trip. Why are your car AC lines freezing up and what you can do about it?

Usually, AC is one of those forgotten systems that you never really think about until it stops working. Sometimes there can be worn or unmodified AC systems that function for years without a problem. On the other hand, if your car has been in an accident, has ever had any AC components removed or had any service done, the situation is ripe for frozen AC lines.

What causes car AC lines to freeze up?

Really, the only thing that should be in your car’s AC system is refrigerant and oil. To keep these things inside and others — such as air, moisture and dirt — out, the pipes, hoses and seals are specially designed to maintain a tight seal. The problem of car AC lines freezing up is caused by moisture that has been introduced into the system. At the expansion valve or fixed orifice tube, depending on the system, liquid refrigerant quickly expands into a gas, forcing the temperature to drop. Moisture in the system can freeze at that point, blocking refrigerant flow through the valve, and you’ll notice you have warm air coming out of the vents. As the valve warms up again, the ice melts and refrigerant flows, so you’ll get cool air again, but the cycle will continue.

Generally, the only way that moisture can get into the AC is if the system is opened up or if you have a leak. If there is a leak, air and moisture can be pulled in by vacuum on the low side of the system. Also, any time that the AC system is opened, moisture can get in. For example, if you fill up the system yourself with an R-134a top-off bottle, a little moisture can get in when you open the valve cap and install the can. There is also no way to accurately determine how much freon the system needs when you fill the system yourself. Overfilling causes as many problems as low freon. AC systems perform best when the refrigerant is at the recommended level. There isn’t a lot of wiggle room here. Similarly, if an accident breaks the system, such as the condenser or one of the lines, the open system can freely absorb water from the air. Normally, the receiver-dryer absorbs some of this moisture, but it only has so much capacity before it is saturated, leaving the rest to float about in the refrigerant stream. If the system has been opened for more than a few hours from an accident, damage or corrosion, the receiver-dryer must be replaced.

What can you do about moisture in the system?

If you notice your car AC lines freezing up, you have to get rid of the moisture that’s causing it, starting with a full leak check. It is best to have an expert technician check out your system. Before your refrigerant is replaced, the service technician will test the unit. An ultraviolet dye will be injected into the system which allows the technician to detect any leaks that are present. The technician will also test or inspect the other system parts such as the condenser, receiver-dryer, O-rings, hoses, lines or evaporators for blocks or leaks and diagnose any issues. Once the system has been inspected and parts replaced if necessary, the system is finally ready to be recharged with the proper quantities of refrigerant, oil and a little ultraviolet dye for future leak detection. For the recharge part of the service, the technician attaches a special machine to the air conditioning unit which accurately dispenses the freon to just the right level.

Take advantage of Don’s ProTechnology’s A/C Service special for $119.95 (for most cars) and mention the coupon you saw in The Loop newspaper. To make an appointment or chat with one of the knowledgeable service advisors or technicians at Don’s Pro Technology Automotive Repair, visit the shop at 230 E. Tehachapi Blvd., or call (661) 822-1600.

The next time you feel a refreshing blast of cool air coming from your vent, you can thank Willis Carrier, the inventor of electrical air conditioning.


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