Our Favorite Online Repair Manual... Mitchell1
WAIT, BEFORE YOU SCROLL DOWN! While I know a lot about cars, I don't know a lot about YOUR CAR! A repair manual is essential for troubleshooting HVAC issues.

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On The Road

Getting Hot?

Nothing stinks more than having your Air Conditioning go out while on a long summer trip. Of course I could tell you to get the system checked BEFORE you ventured out, but what good would that do now? There is not much you can do while driving to help when your A/C system has pooped out on you. There are a few things you could check though... make sure the condenser is free from obstructions (usually sits right in front of the radiator.) Check belt tension for the compressor, and make sure the clutch wiring is connected properly.

Fan only blows two speeds, OFF and Full Bore?

Most likely your resistor is shot. The fan circuit has a resistor which controls the speed of the fan blowing air through your vents. When they go bad, you only have one speed, full blast. Usually an affordable fix, the hardest part is finding the location of the resistor under the dash.

Online Repair Manuals

The HVAC system is complex to say the least. You need a repair manual to guide you to the specifics of maintaining and repairing your HVAC system. Checkout Mitchell1 for the best online repair manuals.

The HVAC System

How your heater and Air Conditioning A/C Works.

Without the heating and air conditioning systems in today’s modern vehicles, we would all be miserable driving to our destinations. We take for granted the heat that keeps us warm in the winter months, and the cool air that refreshes in the summer time. Let’s take a look at how both systems work to keep us comfortable all year round.

The heater in your car is basically a smaller version of your cooling systems radiator. Hot engine coolant is circulated through a small radiator, often times called a heater core. A fan is positioned in front of the heater core to blow cold outside air over the fins. As this air travels over the heater core, it heats up and becomes the hot air which blows out your heater vents.

Like your engines cooling system radiator, the heater core can suffer some of the same issues. If the heater core becomes clogged with rust or sludge, you will no longer have heat. Also leaks can cause a cabin full of white steam and really mess up your windows. If you smell the sweet aroma of coolant when your heater is on, chances are, you have a small leak in the heater core. Often times the heater core is buried under the dashboard, and replacing it, is a major job.

The air conditioning system in your car is comprised of a compressor, condenser, expansion valve and evaporator. If you have ever used a can of compressed air to clean computer components, you will know that the bottle gets very cold in a short amount of time. This is due to the rapid expansion of the compressed gas. The same thing happens in your car’s air conditioning system. Refrigerant (AKA Freon) is compressed in the compressor and turns into a hot gas. In the condenser, this hot gas is cooled to a liquid state and travels to the expansion valve. As the Freon goes through the expansion valve it returns to a low-pressure gas and rapidly cools in the evaporator. A fan blows over the evaporator and cools the air that eventually blows out your vents. It's critical to have good procedures and diagrams when troubleshooting your HVAC system, in days past you would grab a printed manual but now they are available online!

Common Problems:

  • From time to time the A/C system needs to be recharged to bring it back up to maximum efficiency. Sometimes a leak may cause loss of refrigerant and will need to be fixed before refilling. It's difficult to tell if a leak is present without specific test equipment so let it up to a professional.
  • In recent years, the EPA has phased out the use of R-12 Freon in all refrigeration systems and R-134 has become the new standard. If you have an older system with R-12 you may need to retrofit your system to handle the new R-134 refrigerant. Sometimes seals, hoses and even the compressor need to be changed. The problem arises when the older seals and hoses are not compatible with the new oils found in the R-134.
  • Corrosion will cause the heater core (secondary radiator) to leak. This will manifest itself by leaving steam into the passenger compartment and fogging your windows. You will know there is a leak by the sweet smell coming from your vents. Unfortunately changing the heater core is usually not the easier job in the world as engineers tend to squeeze them into some pretty tight spaces under the dash.

Where to next?