ACtion Magazine - September/October 2011 - (Page 20)

Basics training And in this case, perhaps very basic. Forgetting to check the simplest and often most logical causes may send a technician down a long and unproductive road. Heat exchange works on some very simple principles—forget them at your peril. For example: you cannot “make” cold—you can only remove heat. How, and how well (or efficiently), that heat is removed determines the cooling effect. Additionally, everything is proportional; that is, the amount of heat to be removed should be considered as well. An excessive heat load at the source can simply overwhelm the system designed to cool it and it’s not the system’s fault. Heat exchange also works both ways, and a system may add heat instead of removing it. Underheating can be a significant problem in many areas. An obvious example is the passenger cabin on a cold morning, but heating elements for hybrid battery packs are another example. As emission and fuel mileage requirements put a much sharper point on thermal management, diagnosis only becomes more confusing. While you’re hooking up the scan tool, be thinking about these basics. What’s going on here? What is supposed to be cooled (or heated), what is the heat source, and is there enough media present to carry the heat load? It should be obvious, but low fluid levels can cause a lot of problems. Remember that engine oil provides roughly a third of engine cooling. Low refrigerant may cause the pressure switch to open and lock out the compressor, but we’ve all seen systems that are just above the trip point. They work, but not well enough. Additionally, whatever is in the system needs to be correct for the job. You wouldn’t put 10w-40 in a differential or R-718 into an R-134a system. Why put in the incorrect antifreeze? With modern vehicles it’s also not impossible to be confronted with a heat problem originating from fuel lines, or trans and final drive lubricants. Heavy-load or high performance vehicles may have cooling systems for those components as well. And as turbo and supercharging becomes more common, you’ll also meet charge air coolers in the engine bay. Can the cooling medium (air, water, refrigerant, oil) do its job? Once you know you have enough cooling media to carry heat away from the source, can the coolant exchange its heat at the other end? How will it get there? Many cooling systems use a pump to move the media, whether it is a water pump, a fuel pump or a compressor. Besides your test equipment, always remember to use the proven “Mark-I Eyeball system” on any pump because no scan tool will show you slipping belts, loose mounting bolts or a burned clutch. Most heat exchangers (but not all) use airflow to pull heat away from the cooling media. Can the air get through the fins? As front-end heat exchangers become packages, with many coolers in one unit, there are more and more places for dirt, leaves and road trash to hide. How many pictures of clogged or damaged condensers will it take to convince someone to spend a minute looking at the front of the car? Five minutes with a garden hose may be time well spent in a lot of cases. Well, it’s mostly air cooling, and there’s plenty of air around, right? Yes and no: can that air get to and from the heat exchanger? As much as we hate them, all those spoilers, scoops Chevrolet’s Volt has three distinct cooling systems and you have to know what each does. 20 ACTION • September/October 2011 Today’s multiple, tightly packed coolers require unrestricted airflow.

Table of Contents for the Digital Edition of ACtion Magazine - September/October 2011

ACtion Magazine - September/October 2011
Table of Contents
Outlook
Expansion Valve
Techncally RELAY-ted
Under The Southern Cross
Leonard’s Law
News & Updates
Virtual View
Cooling Corner
Performance Always Needs More Cooling
ACDelco’s Guidelines for Replacing Engine Coolant
Worldwide Training
New Member Profile: Alex Original, Ltd
Association News
Obituary
Quick Check
New Products & Services
Last Watch

ACtion Magazine - September/October 2011

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