When I mention “electrical” problems, I’m not referring to electronics. That’s a different topic all together in my book! To me, electrical is typically anything that’s not involving a computer. To clarify more, electrical may include the wires and terminals leading up to a module, but not necessarily the module itself. We’ll have opportunities to share war stories involving faulty electronics at some point in the future.
At almost every automotive training class I attend — and at the ones I present — at almost every trade show and at just about every technician gathering, it is inevitable someone will share (with anyone who will listen) a diagnostic dilemma in which they are currently involved or had recently encountered. It is in our nature to share them I think, but not so much to beat our chests (in most cases), but instead to possibly learn how better we can diagnose such a problem in the future. In almost every case, you’ll hear how much longer the solution took to find than the story-teller thinks it should have, had they encountered something similar previously.
I’ve not seen everything there is to see and I pity the poor soul who thinks they have when it comes to automotive electrical problems. I attend as many training events as I can in part to hear other people’s war stories. My feeling is, if it happened to that person, it will likely happen to me as well and when it does, I’ll have an advantage – that I learned how it was solved without suffering the pain and agony that the other person went through! I am a member of many automotive technician websites for the same reasons. There’s no logical reason for me to work harder than I have to. Is there one for you?
In my classes I try to emphasize the importance of understanding the concepts, the strategies and the principles of operation rather than to focus on how any one manufacturer has applied those to their products. What I mean is, for example, it’s great to know how a GM TPS (Throttle Position Sensor) works, and it’s important to know how to properly test it. It’s as important to know where each one may be located on the various applications ONLY if the majority of vehicles on which you work are manufactured by GM.
However, most of us do not work on only one brand of vehicle. So, if you know the principles of operation for a GM TPS, for example, then no matter which manufacturer employs a similar device, you should still be able to apply the concepts learned about the GM TPS to the one you are working on today. There are rare exceptions but a majority of TPSs, a majority of starters, a majority of fuel injectors (etcetera) — all share the same concepts. Master those concepts and apply them to whatever you’re fixing today to be considered a great diagnostician!
Applying electrical principles
I recently had an opportunity to put my own instruction to the test on a non-automotive application. Some good friends, a married couple, had called a residential heating and air specialist because their home HVAC (Heating, Ventilating and Air Conditioning) unit would blow air properly but not always at the correct temperature. The HVAC technician spent less than a half an hour after arriving to inspect the unit before presenting my friends with the recommendation to replace the whole thing. He claimed it was very old and inefficient and said he’s not familiar with that brand, then said he wasn’t trained on them anyway. It didn’t cost anything for his service call nor for his writing an estimate for replacing the unit (thankfully!). I suppose we consider 1999 cars as “very old,” which is the same year this HVAC unit was produced. I’ll give the tech that much.
When my friends told me of their dilemma and what the tech had said, I just shook my head in shame, knowing a lot of automotive technicians say similar things to owners of vehicles on which they were not trained. The HVAC technician could have applied the same concepts he knew to this (well-known) brand, but apparently didn’t have confidence in his skills to attempt such a thing. It seems more of us at least attempt to apply the principles of operation on vehicles we may not be familiar with. The HVAC technician never even tried.
Being the brave soul that I am, I told my friends I’d look at it and see what I can do. I started by researching the complaint for the brand and model on a few DIY home repair and HVAC websites. I wanted to see if there was something that went wrong commonly with units that were similar to my friends’. This is no different than one of the first steps I’d perform when researching an automotive problem on a brand with which I was unfamiliar. Do you use websites like iATN, Identifix, Diagnostic Network, etc.? I find these extremely valuable especially under the same circumstances.
I didn’t have any good luck. There weren’t enough identical complaints/fixes for me to condemn any particular component based on a common problem. There were no silver bullets for me here. I had to consider doing what a good HVAC technician might do – diagnose it!
My research led me to the manufacturer’s website where published were the complete wiring diagram, the Owner’s Manual, a Quick Start Guide and get this, an installation manual complete with a troubleshooting guide! How about that? This very old unit has built-in troubleshooting complete with blink-out codes!
You younger folks might not appreciate my excitement, but having been present when cars were finally equipped with self-diagnostics, it completely changed the much-lengthier diagnostic processes we had to perform prior to that improvement! Imagine what we went through when working on computer systems that were not equipped with a way to direct you to a system, let alone a component that may be faulty?
As typically happens when working on cars with an intermittent fault, when I arrived to look at the HVAC unit, it was working as designed. Also as expected, this very old unit had no ability to store codes, just like the very old cars that erased codes when the key got turned off. This is where my diagnostic instincts came into play.
I looked at the wiring diagram to understand the circuits – excluding the air distribution section (remember, the home owners said it continued blowing, just not always at the desired temperature). In the diagram was a compressor “Contactor” which looked similar to the way a car’s starter solenoid would be wired. Knowing how an intermittent “No Crank” complaint was sometimes attributed to the starter solenoid I headed in that direction.
With BOTH circuit breakers tripped, I removed a service panel. Once the unit’s cover was off I performed a visual inspection and saw almost every serviceable component well within reach – unlike what we encounter on cars – and in plain view was the Contactor and just about everything else. It was obvious there had been a lot of arcing of the contactor plate, which required no disassembly for me to measure voltage drop across the circuit when operated. I carefully attached the best meter I have to the terminals on each side of the Contactor, then I operated the compressor repeatedly while observing the meter’s readings (from a distance – I don’t like 220 Volt systems). Not once in the 10 times I turned it on, did I see the same voltage on each side if the contactor. Just like when a starter solenoid fails, the contacts had worn out!
The original equipment (OE) manufacturer had stopped making that part several years ago and listed it in their catalogs as obsolete. I found two aftermarket Contactors that were the same size, same shape, had the same number of terminals but had a higher amperage rating than the OE part. I bought them both for less than $50, including shipping. After verifying identical circuitry to the HVAC unit, I installed the better-looking (higher quality) Contactor and ran the same voltage drop test again. This time the test results were identical, every time, I was confident their unit would work as designed for many more years to come. I like to verify that my test results differ from previous readings after a component replacement. Do you?
To date there have been no more complaints of intermittent operation. As a side note, this HVAC unit had an optional feature that could have been enabled had the wire terminal not been damaged that allows the feature. I replaced the terminal, connected it appropriately and have some very happy (and comfortable) friends again! I’m not a HVAC technician but I was able to accurately apply the concepts I learned in the automotive repair trade to successfully repair a residential HVAC unit.
Principles of induction
I was a dealership diagnostic technician who was presented with a particularly challenging diagnostic dilemma in one memorable diagnostic battle that occurred early in my career. One of the first redesigned Chevrolet Corvette models to be delivered to the public (at that time) had been purchased by the dealership’s owner’s son. The car returned with an A/C blows warm air complaint in less than a week after initial delivery.
The compressor fuse had opened the circuit it protected, but whatever had caused it to do so was not evident. A new fuse was installed and the car returned to its owner. Within a week the same thing happened, with the same test results and the same repair. You know what happened again, yes, the car returned. I was instructed to locate the cause and to repair it before taking on ANY other job. When you work in a flat rate environment, you do not like hearing instructions like that, ever! Knowing it was the owner’s son’s car also made this job extremely important.
In the early 1980s we didn’t have all the fancy diagnostic tools that are available today. What I had to work with were made by Radio Shack, Sears & Roebuck and a few miscellaneous items bought from tool truck vendors. Does that give you any idea what kind of challenge this intermittent fault presented?
In short, at the 10-hour (into it) mark, my service manager enlisted the assistance from techs at other dealerships. I knew how to reproduce the blown fuse but we couldn’t determine what was causing it. The blower had to be in M2 speed, the third fastest selection, for about 15 minutes but visual inspection of the circuits involved did not reveal any shorts. We isolated wiring, jumped circuits, replaced several components, etc., etc. with no positive effects.
At the 20-hour mark, (over the phone) assistance was requested from the GM engineers. We followed their directions to no avail. At the 30-hour mark, two instructors were flown in from a GM training center several hundreds of miles away. They flew back by the end of the week dumbfounded. After that, two engineers were flown in from either Bowling Green, Ky., or Detroit, Mich. (or both, I don’t remember).
Meanwhile, not having received a decent paycheck since this job started, I was getting poorer by the week. These two gentlemen came on the scene like gangbusters, were full of ideas (none of which hadn’t been tried yet) but after the fourth full day, were as flabbergasted as all the rest who had touched this car. They went to lunch with the service manager and for a change, I left the premises too. I went to a nearby park, sat under a tree and processed everything that had been done over the past several weeks. I got away from the car – and figured out what was causing the problem.
Upon arriving back from lunch the engineers were not sure in which direction we would proceed. I told them to go to their respective homes and that I had it figured out. Of course, everyone was excited and wanted to know what was causing that fuse to blow. I refused to say unless I was guaranteed to receive payment for every hour I had invested (by then, 48 hours!). At first the service manager balked, said something about not being able to promise that. I replied there were several thousands of these cars built the same way that will dumbfound a lot of people — and if THAT wasn’t worth the money I should have earned then I was walking! The engineers convinced the service manager to change his mind.
You’re wondering too, aren’t you? Here we go...In M2 speed, the blower resistor is using all of its resistors, glowing cherry red. A lot of amperage is flowing through that circuit. At that blower speed, with all the windows closed, after about 15 minutes the low-pressure side of the air conditioning system drops and the (axial) air conditioning compressor cycles off. When it cycles back on, the total amperage requirements of the alternator exceeded the voltage regulator’s abilities to work properly.
This vehicle was equipped with an Amp gauge which was wired IN SERIES with the alternator output. Between where the heavy (10 Gauge?) wiring passed through the “Firewall” (Bulkhead) connector to and from the Amp gauge, was located the air condition compressor clutch circuit wire. It was basically sandwiched between both of the Amp gauge’s wires.
During the momentary alternator overload condition, amperage was induced into the A/C compressor clutch circuit — which subsequently caused the fuse to blow (open the circuit). Relocating the smaller wire in a different position of the bulkhead connector solved the problem.
I repeated the blown fuse, and proved the repair, multiple times for the benefit of the engineers before they left. Like I mentioned earlier, I want to test the repair repeatedly in order to confirm the problem is fixed. I got paid for every hour I invested in that car and never forgot about induction again. I’ll bet those two engineers didn’t either!
