Timely Topics Archive

A Monthly Article for Vigor Enthusiasts (10/02)


A/C System (R-12 to R-134a) Conversion


This month we’re going to look at a job that every Vigor owner will have to consider sooner or laterconverting the A/C system from one using R-12 refrigerant to one using R-134a refrigerant. The info here comes from a fellow named "Mat."

First, let’s take a look at the overall A/C system and see how it works. Refer to the illustrations below.

 AC System Schematic

The system is filled with a gas called a refrigerant. Vigs use a refrigerant called R-12. The refrigerant in the system is compressed in the compressor. Anytime a fluid (i.e., a gas or a liquid) is compressed (whether it’s air or R-12) the gas heats up. So now we have a compressed high-temperature gas in the A/C lines. This is known as the high-pressure side, or simply the high side.

Vigor A/C system


Vigor A/C System


The high-temperature, high-pressure gas enters the condenser, which is like a radiator, where it gives off its heat to the air passing through the fins. It’s cooled off enough to turn it into a liquid. Then, the high-temperature, high-pressure liquid goes to the receiver dryer, where any water is removed.

From there, the liquid travels through lines inside the car, under the dash, where it reaches the evaporator core. As the gas enters the evaporator core it passes through an expansion valve, and this is where the coldth comes from. (Hey! If we can have warmth, we oughta have coldth.) The high-pressure refrigerant goes from a high pressure (in the range of 200-300 psi) to a low pressure (in the 50-60 psi range) as it passes through the expansion valve. We learned in high school physics that, when any fluid (i.e., gas or liquid) goes from a high pressure to a low pressure, it becomes colder. The cold fluid is then routed through the evaporator core (this section is called the low-pressure side, or simply the low side).

The blower motor fan blows air through the evaporator (it’s essentially another radiator). As the air passes through the cold evaporator core, it cools off... and the cool air is routed through the ductwork, where it blows on you and cools you off.

The refrigerant is then routed through lines back to the compressor and the process starts again.

Why Convert?

Over time, the A/C system will eventually lose pressure and not produce as much coldth as it should. The cure is to add more refrigerant until the pressure is back to normal. The problem is, R-12 is a chloro-flurocarbona CFCand although it's never been proven, a lot of folks think that CFC's are harming the Earth's ozone layer. Whether you believe the United States EPA (which claims that CFCs are destroying the ozone layer) or NASA (which claims the ozone layer hasn't changed since they began measuring it), the point is moot. The EPA has disallowed the use of R-12 refrigerant in newer cars and that's that!

As a result, auto manufacturers have switched over to a non-CFC refrigerant called R-134a, and R-12 is becoming rare ...and expensive! In fact, it's so expensive that it's cheaper to convert to R-134a than it is to top up your Vig with a few ounces of R-12.

The Conversion Kit

Conversion Kit


R-12 to R-134a Conversion Kit


Fortunately for us, everything in a Vig's R-12 system is compatible with R-134a.

This means we won't have to buy a new compressor, or new hoses, or anything. All we have to buy is an R-12 to R-134a conversion kit (see photo at right).

These kits are available at most auto parts stores. They usually contain everything you'll need to do the conversion, although this particular kit contained everything except the R-134a, which had to be purchased separately.

This kit contains...

  • Two fittings (and three dustcaps)one for the high side and one for the low side. R-12 and R-134a use different fittings so you can't mix the two. The dustcaps are for the fittings. (The third dustcap is used to cap the can of refrigerant if there's any left over.)
  • A hose to connect from the cans to the fittings
  • A can of oil that lubricates the compressor
  • A sticker that identifies the system as an R-134a system and not an R-12 system.

The Conversion Process

High Side

High-Pressure Fitting


The conversion described here was done by a fellow known only as "Mat." He's not a club member, but he was good enough to provide the information and pics for this article. Thanks, Mat!

The first step is to purge the system of all the old R-12. By US law, the R-12 must be recovered by a "certified" air conditioning tech with "approved recovery equipment." If you just let the R-12 vent into the atmosphere, and an Eco-Nazi reports you to the authorities, The State can put you in jail and take your money away from you. Not good!

If you're friendly with an A/C tech, he may be willing to evacuate your system at no charge. After all, he gets to keep the R-12, and R-12 is expensive.

Once the system is free of R-12, you're ready to use your kit.

If you're like most Do-It-Yourselfers, you probably won't be doing anything to the high side of the systemin fact, Mat didn't even bother to install the high-side fitting. It's only function during a conversion is to attach a set of gauges which none of us probably has anyway.

So all the work will be done on the low-side.

Add 134a

Add R-134a to the Low-Side


First, remove the low-side fitting, screw in the new one, and add a can or two of R-134a to the low-side using the hose, as shown in the photo at right. The fittings are "quick connect" couplersthe new fitting is a male  and the hose has a female connector. On the hose, slide the sleeve back, push it on to the male fitting, and release the sleeve.

Next, add the oil charge to the same fitting, as shown in the photo below.

Then, add the balance of the R-134a.

There's a bit of complexity involved here, but not much. The Vig's R-12 capacity is 28 to 30 ounces. R-134a should be installed at 10 to 15% less than R-12, or roughly 24 to 27 ounces.

Mat used two 12-ounce cans of R-134a. It also comes in 3, 5, 7, 13, and 16-ounce cans, so if you want to get creative, you can obtain just about any charge you want by buying various combinations.

When you're through, put the dustcap(s) on the fitting(s). The standard color code is Red for the high side and Blue for the low side.

Finally, put the sticker on, so anyone who services your A/C will know that it has R-134a.This is also required by law in the US.

Add Oil


Add Lubricating Oil to the Low-Side


Two things to keep in mind:

  1. Mat claims the new R-134a refrigerant doesn't cool his car quite as much as the old R-12 did. Almost... but not quite. It isn't known whether Mat actually measured the outlet temperature with a thermometer or whether this is a subjective impression.
  2. Bubbles in the sight glass are normal.

Also, for you general font of knowledge, most auto manufacturers generally strive for a 20 difference between ambient (outside) air and cooled air.








Biker Bil advises that you should...

"... replace the compressor with a NEW one that is already prefilled with PAG oil, and the system must be completely disassembled and flushed properly. That means removing your evap. No easy task.

"This assumes that you want your conversion to remain trouble free for years. Axe if you have questions.


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