Diagnosing Computer Controlled HVAC Systems

Computer Controlled HVAC Pre OBD II Vehicles built prior to the advent of OBD II¬†typically used electronic control modules only to operate their automatic temperature control systems. On these models, the control module was typically contained in the HVAC control head in the same unit housing the driver’s system control switches. Warning indicators may or may not be included on… Read More

A/C System Performance Testing Part 2

A/C Performance Testing A performance test can determine whether the A/C system is functioning properly and if it is not can indicate what is wrong so the system can be repaired.Different vehicle manufacturers specify different methods to conduct system performance checks, but as a guideline, the following procedure may be used.Connect a manifold gauge set as previously described. Hang the… Read More

A/C System Performance Testing Part 1

Automotive Refrigerants The refrigerant used in automotive air conditioning systems from their inception until the early 1990s was a chemical compound called dichlorodiflouoromethane, more commonly known as Freon or R12. R12 is a member of the chemical family known as chlorofluorocarbons(CFCs). Although R12 works extremely well as a heat transfer medium in an automotive air conditioning system, CFCs have been… Read More

Volkswagen Instrument Cluster Failure

Over the years of working on VW’s I have encountered enough instrument cluster failures that I would consider it a common problem. There are a few things you should be aware of before attempting to repair this unit. Don’t Buy Used VW Cluster I have tried this route already and have been burned multiple times. The bad part about it… Read More

Variable Valve Timing Systems

Why Use Variable Valve Timing? Increased Volumetric Efficiency Reduction of Pumping Losses Lower Parts Count More efficient Variable Valve Timing or VVT is common on most engines and is responsible for the elimination of many EGR valves as well as increased performance and fuel economy on many engines. Most systems are lube oil activated and use a control solenoid as… Read More

Honda Automatic Transmission Failure

Honda AT transmissions are common to have failure and I have rebuilt many of these over the years. Most transmissions have a pan you can remove and service the filter, which is a common service at around 30K to maybe 60K depending on the manufacturer and type of fluid ran in the transmission. Honda automatic transmissions have a closed case… Read More

A/C System Operation

A/C System Basic Principles In order to understand how an A/C system works, we must first understand a few basic principles. The first, and most important principle is that heat always moves toward a state of less heat. This is how an engine’s cooling system works. Heat created by the combustion process in the engine’s cylinders is transferred to the… Read More

Brake Proportioning Valve Operation

The proportioning valve is installed on vehicles with front disc rear drum braking systems. It is installed in the hydraulic line leading to the rear drum brakes and helps prevent rear wheel lock up. Many proportioning valves are mounted directly in the master cylinder outlet to the rear brakes. They provide balanced braking during panic braking situations or when the… Read More

Limited Slip Differential Operation

Limited slip differentials lock two wheels together while traveling in a straight line. While cornering it allows for the outside wheel to rotate faster than the inside by overcoming the tension of a clutch. The clutch type differential is the most common and consists of two sets of multiple disc clutch packs located on each of the two side gears.… Read More

Charging System Voltage Regulation

At the heart of the automotive electrical system is the alternator. Without voltage regulation the alternator would consistently produce too much voltage overcharging the battery and causing damage to the electrical system itself. Alternator charging voltage can be regulated using an electro-mechanical, electronic, or computer controlled regulator. Most late model vehicles use computer controlled regulation. This is when the function… Read More