A/C: Converting To 134A

GM Upgrades: Keep it Cool!

Converting to 134a

Courtesy of Classic Auto Air   Classicautoair.com

Until 1995, most cars with air conditioning used R-12 Freon refrigerant that is said to have a negative side effect of damaging the ozone layer and is no longer produced in most countries. Now, the industry standard is R-134a, which is an efficient absorber and carrier of heat without the ozone layer-damaging issues of R-12. Contrary to popular belief, most cars originally equipped with R-12 can be converted to 134a and still keep you just as cool.

Recommended steps to converting your GM R12 air conditioning system to 134a:

1955-61 Models with Hot Gas Valve (aka Bypass or Hot Gas Bypass Valve)

The Hot Gas Valve is most often found mounted to the compressor, though some cars have it mounted back near the evaporator. The front half of it looks like a bullet.

Minimum Requirements

• Change or restore the filter-drier.
• Drain the compressor oil and recharge with 134a compatible oil. (PAG or Ester Oil)
• Ensure that the system is clean and free of contaminants (Depending on component condition, this may be a simple matter of blowing out with compressed air or liquid flushing with an air conditioning flushing agent)
• Replace or restore all rubber hoses with barrier hose.
• Rebuild hot gas valve.
• Install 134a charge port adapters.
• Charge with 134a between 70-80% of the original R12 charge amount. Note: Hot gas valve will need to be adjusted during the charging process to properly adjust the low side bypass pressure to 20psi.
• Replace any o-rings with 134a compatible.

 Recommended:

• Install hi/lo pressure switch

 Helpful hints:

• Ignore the sight-glass. A properly charged 134a system will likely show bubbles in the sight-glass.
• Typical 134a charge rate will be approximately 70-80% of the factory R12 charge amount.

1962-66 Models with Suction Throttling Valve (aka STV)

The suction throttling valve is installed on the evaporator, near the firewall.

 Minimum Requirements

• Change or restore the filter-drier.
• Drain the compressor oil and recharge with 134a compatible oil. (PAG or Ester Oil)
• Ensure that the system is clean and free of contaminants (Depending on component condition, this may be a simple matter of blowing out with compressed air or liquid flushing with an air conditioning flushing agent)
• Replace or restore all rubber hoses with barrier hose.
• Rebuild suction throttling valve.
• Install 134a charge port adapters.
• Charge with 134a between 70-80% of the original R12 charge amount. Note: Suction throttling valve will need to be adjusted during the charging process to properly adjust the low side bypass pressure to 20psi.
• Replace any o-rings with 134a compatible.

 Recommended:

• Install hi/lo pressure switch

 Helpful hints:

• Ignore the sight-glass. A properly charged 134a system will likely show bubbles in the sight-glass.
• Typical 134a charge rate will be approximately 70-80% of the factory R12 charge amount.

1966-73 Models with POA Valve

The POA Valve is installed on the evaporator, near the firewall.

Minimum Requirements

• Change or restore the filter-drier.
• Drain the compressor oil and recharge with 134a compatible oil. (PAG or Ester Oil)
• Ensure that the system is clean and free of contaminants (Depending on component condition, this may be a simple matter of blowing out with compressed air or liquid flushing with an air conditioning flushing agent)
• Replace or restore all rubber hoses with barrier hose.
• Install 134a charge port adapters.
• Send POA valve in to be calibrated
• Charge with 134a between 70-80% of the original R12 charge amount.
• Replace any o-rings with 134a compatible.

 Recommended:

• Install hi/lo pressure switch

 Helpful hints:

• Ignore the sight-glass. A properly charged 134a system will likely show bubbles in the sight-glass.
• Typical 134a charge rate will be approximately 70-80% of the factory R12 charge amount.

1973-76 Models with VIR

The VIR is installed on the evaporator, near the firewall.

 Minimum Requirements

• Change desiccant in VIR.
• Drain the compressor oil and recharge with 134a compatible oil. (PAG or Ester Oil)
• Ensure that the system is clean and free of contaminants (Depending on component condition, this may be a simple matter of blowing out with compressed air or liquid flushing with an air conditioning flushing agent)
• Replace or restore all rubber hoses with barrier hose.
• Install 134a charge port adapters.
• Charge with 134a between 70-80% of the original R12 charge amount.
• Replace any o-rings with 134a compatible.

 Recommended:

• Install hi/lo pressure switch
• Install our VIR Eliminator (strongly recommended when converting to 134a), purchase a rebuilt VIR or let us, Classic Auto Air, rebuild yours.

 Helpful hints:

• Ignore the sight-glass. A properly charged 134a system will likely show bubbles in the sight-glass.
• Typical 134a charge rate will be approximately 70-80% of the factory R12 charge amount.

1977-94 Models with Accumulator

The accumulator is most often installed on the evaporator, near the firewall.

Minimum Requirements

• Change or restore the accumulator.
• Drain the compressor oil and recharge with 134a compatible oil. (PAG or Ester Oil)
• Ensure that the system is clean and free of contaminants (Depending on component condition, this may be a simple matter of blowing out with compressed air or liquid flushing with an air conditioning flushing agent)
• Replace or restore all rubber hoses with barrier hose.
• Install 134a charge port adapters.
• Charge with 134a between 70-80% of the original R12 charge amount.
• Replace any o-rings with 134a compatible.

 Recommended:

• Install hi/lo pressure switch
• Upgrade the standard orifice-tube to a variable orifice tube.

 Helpful hints:

• Ignore the sight-glass. A properly charged 134a system will likely show bubbles in the sight-glass.
• Typical 134a charge rate will be approximately 70-80% of the factory R12 charge amount.