Bottom Line
Maintenance Q&A
Stinking trucks and LED labyrinths

Paul Abelson
Senior Technical Editor

Question: My truck stinks. I don’t mean I don’t like it, I mean it smells awful from the air conditioner and heater. I sprayed everything from air freshener to Lysol into the vents and nothing helps. With winter coming, I don’t want to have to keep the windows open. Help!

Answer: This is an all-too-common problem, because of mold and mildew. When air conditioners chill the air passing over the evaporator, they reduce the air’s ability to hold humidity. Moisture condenses and most of it drains from the vehicle. That’s why you see water dripping from cars in summer. Some of that water stays on the evaporator’s fins. As the truck warms, mold spores from the air find a home in the moisture. In quite a few trucks, the mold multiplies and forms colonies on the fins.

I don’t know why it happens in some trucks but not others, but I do know what to do when it happens. It may be because drain lines are clogged or pinched. Make sure your drain is clear.

Since the mold is in the evaporator and heat exchanger portions of your HVAC system, you’ve got to take the cover off and treat the evaporator and heater core with a fungicide. Fungicides are fairly toxic chemicals. Their application and use are governed by EPA regulations. There are some diluted chemicals available for do-it-yourself use, but they require multiple applications over several weeks. This is one case where you’ll probably be better off having the work done by a licensed pesticide technician. Many HVAC shops have one on staff or on call.

Question: I switched to LED lights on both my 1998 tractor and 1999 trailer. They look better, and I’ve read that they last longer. There’s only one problem. My flashers and turn signals won’t work. I’ve been flicking the indicator up and down for signal turns, but that gets old in a hurry. Besides, I have no four-ways. I changed flashers twice and even took one from a friend’s (similar) truck. They work in his truck but not mine. What gives?

Answer: One would think that something as basic as flashers would be standardized by now, with variations for the number of lamps and not much more. But today there are many, many types and styles of LEDs on the market. There are fixed load, variable load, and from two to 10 lamps per side. There are electromechanical flashers and electronic flashers.

You said that each side of your tractor-trailer combination has two front turn lights, two 4-inch stop/turn/tail lights on the tractor, two more on the trailer, and mid-turn signal. That’s seven lamps per side. At 2.1 amps per bulb (per TMC RP143), your old set-up drew 14.7 amps total. With LED replacements, that current draw is down to 3.5 amps. 

Your original flashers and the replacements you got were mechanical. These flashers have a bi-metallic strip fixed at one end and making contact at the other end. As current flows, the two metals heat up and expand at different rates. That makes the strip curve away from the contact. Current stops flowing, letting the strip cool down. It straightens and again makes contact. Then the process repeats. When the current flows, your turn signals are on. When contact is broken, they go dark. 

Fourteen amps is more than enough current to heat your old flasher. But the 3.5 amps the LEDs draw is not. Current continues to flow and no flashing occurs. Most, but not all electromechanical flashers work with 2 amps or more. Some require more than 5 amps. Your flashers evidently needed the high amperage. Electronic flashers work at 1 or 2 amps.

Question: I had an accident, which, among other damage, bent my steering axle enough that it was no longer within component and vehicle tolerances. The camber tolerance is out. The axle manufacturer says the camber tolerances are machined into the axle at time of manufacture and are not adjustable. The vehicle manufacturer (dealer) is telling me the only way to repair this axle is to bend it back straight, and they cannot do this because the axle manufacturer expressly forbids bending of axle beams in their alignment procedure manual. I have verified this prohibition with the axle manufacturer. There is an independent axle repair shop that says they can align this axle. I am worried about my liability if something happens to this axle if I have it repaired with the prior knowledge of these repair prohibitions. I need advice.

Answer: The last thing you want to mess with is the metallurgy of structural components of your truck. Axles are heat treated and tempered to have certain properties that the manufacturer designed in. Flex and resistance to bending are balanced. Steering geometry is machined-in to solid steer axles. 

There are two ways to alter the designed-in properties: heat and mechanical force. You wrote that your axle was bent in an accident. That means that sufficient force was applied to move the metal beyond its elastic limits, giving it a new permanent set. Even if you could cold-forge the axle back to its original dimensions, the crash stressed the axle so it no longer has its original properties. Shops that straighten axles use heat to soften the metal, and force to bring it back into line. The axle may be dimensionally close to the original, but it won’t have the resilience of a new one. 

Under today’s interpretations of law, anyone who alters a vehicle component covered by Federal Motor Carrier Safety Standards becomes, in effect, a manufacturer, with all the liability that goes with it. If the manufacturer said not to bend the axle, but you authorized a shop to do it, they and you have assumed liabilities your insurance companies may not cover. 

A new axle isn’t that much more expensive. Don’t practice false economy with axles. Replace, don’t repair.

Headlight woes revisited
In the October issue, I answered a question from the OOIDA Maintenance Forum about headlights. The member wrote that the only way his low beams worked was if the high beams were on. My reply involved checking switches, wiring and plugs. 

I hate it when I overlook the obvious. Frank Conte, a colleague from Truck Writers of North America and an accomplished truck technician in his own right, contacted me with some added information. 

I assumed it was unlikely that both headlights would blow out at the same time. Frank reminded me that voltage spikes could burn out filaments in a heartbeat. Many drivers crank their engines with their lights on, and that alone can cause headlights – and other lamps – to blow out. It may not happen the first few times, but the filaments weaken each time. Starting puts a very high spike through the entire electrical system. 

On a Kenworth, or any truck with four headlamps, the outboard two have both low and high beams. The inners are high beam only. What the member may have seen was two burned-out low beams, with all four lamps lit on high beam. 

For long lamp life, it’s critical to have lights off whenever cranking your engine, or if you have a sudden voltage spike when connecting batteries for a jump-start.

Paul Abelson may be reached at