[Skip to Content]
Time is Money. Find out more about how this app can revolutionize the way you weight your truck.

Become an A/C Drip Expert

By on July 1, 2017


Sure Ways to I.D. Problems
As you find yourself in the middle of this summer’s upper temperature extremes, it’s a great time to make sure you’re A/C system will survive the rest of the journey.

In the last issue, the focus was placed on the efficiency of modern A/C systems and how a little refrigerant leak can cause a huge problem. I want to remind some of you and perhaps inform others about two other warning signs that will help you identify potential A/C system problems. Any decline in A/C performance should be addressed quickly to avoid costly repairs such as replacement of your compressor.

homer-2Early in my career, I was taught the 1-10-100 Rule, which simply says, “One dollar invested in prevention will save 10 dollars on correction and 100 dollars on failure costs.” This rule has become a guiding principle in training technicians and serving customers. It simply means that if you can detect a problem early and have the repairs performed correctly, you will maximize your uptime and minimize your maintenance and repair costs.


Pay Attention to A/C Drain Tube

Let’s start with something very simple, yet often overlooked—lack of moisture dripping from the A/C drain tube while your vehicle is running and the A/C is turned on. The more humid the atmosphere, the more moisture you should see dripping from that drain tube on the passenger side of your truck under the front floor board or coming out of the lower front side of your firewall.

Do not underestimate what you can learn from this dripping. If the humidity is low, you will see less moisture puddling under your truck. If the humidity is average or high and no moisture is visible, you have a problem. It may be that the tube is stopped up and your passenger-side floorboard is wet. The water must go somewhere, so if the tube is restricted, water will overflow the drain pan or box and make its way inside to your cab floor. No visible moisture running on the groundHomerHogg in humid conditions is a sure sign you have an A/C system that is not functioning properly. This is a quick and easy way to identify a common problem with you’re A/C system.

Your evaporator core inside your truck located behind the glove box, in most cases, must absorb the heat inside your cab. It does this by cycling cold refrigerant through the core. As this cold refrigerant flows through the evaporator, the refrigerant absorbs the heat inside the cab. The heat moves through the aluminum fins and tubes, but the moisture in the air cannot, so the moisture collects on the sides of the evaporator core and drips to the bottom and out through the tube. If your A/C system isn’t absorbing much heat, you will see very little moisture dripping.

Freeze Up is Another Bad Sign

Another reason for lack of moisture dripping from your drain tube is the possibility that the A/C is freezing up. Your evaporator freezes, if it gets to 32º or lower. This is one of the reasons that technicians look at pressures on the gauges when troubleshooting A/C systems. The chemical properties of R134a refrigerant enable us to utilize a pressure-temperature chart to determine what the temperature will be based on what the pressure is.

If the pressure is too low, then we know the temperature in the evaporator is too low, and the moisture on the outside of the evaporator will freeze. I know this can be very technical, but it will help you understand that it is critical for that water to be dripping from the drain tube. It can also help you understand the effectiveness of your system based on relating the amount of dripping with the amount of humidity outside.

To avoid a misdiagnosis, know that moisture on the passenger-side floor may be coolant from a leaking heater core or hose. If it smells like antifreeze and/or you notice your windows fogging with a sticky residue, then you may have an engine coolant problem, and not a stopped-up A/C drain tube. So, keep your eyes on the amount of water dripping from that tube, and perhaps you will identify a problem before it becomes an expensive repair.

Remember, you can always rely on the professional technicians at the next TA Truck Service location along your route to help you diagnose a suspected A/C system problem and keep you cool on the road. Drive safe everyone.

ogg’s Maintenance Matters airs on the Dave Nemo Show (Road Dog Trucking, SiriusXM 146), 8 a.m. ET, the first and third Thursdays of each month.Homer H

Homer Hogg, Manager of Technical Development for TA and Petro, has worked as a truck technician for more than 35 years. He is ASE Master-Certified, a Daimler Certified Trainer, and a member of the Nashville Auto-Diesel College Hall of Fame.homer-2

About Road King

For the professional Driver

Leave a Reply

Your email address will not be published. Required fields are marked *