GM Upgrades
CONVERTING to 134a
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 By Pass or Hot Gas By Pass 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. (Click here for a typical photo)
Minimum Requirements
- Change or restore the filter-drier.
- Drain the compressor oil and recharge with 134a compatible oil. (PAG or Ester Oil)
- Insure 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 by-pass pressure to 20psi.
- Replace any o-rings with 134a compatible.
Recommended:
- Install hi/lo pressure switch
1962-66 Models with Suction Throttling Valve (aka STV)
The suction throttling valve is installed on the evaporator, near the firewall. (Click here for a typical photo)
Minimum Requirements
- Change or restore the filter-drier.
- Drain the compressor oil and recharge with 134a compatible oil. (PAG or Ester Oil)
- Insure 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 by-pass pressure to 20psi.
- Replace any o-rings with 134a compatible.
Recommended:
- Install hi/lo pressure switch
1966-73 Models with POA Valve
The POA Valve is installed on the evaporator, near the firewall. (Click here for a typical photo)
Minimum Requirements
- Change or restore the filter-drier.
- Drain the compressor oil and recharge with 134a compatible oil. (PAG or Ester Oil)
- Insure 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
1973-76 Models with VIR
The VIR is installed on the evaporator, near the firewall. (Click here for a typical photo)
Minimum Requirements
- Change desiccant in VIR and remove the POA valve.
- Drain the compressor oil and recharge with 134a compatible oil. (PAG or Ester Oil)
- Insure 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 rebuild yours.
1977-94 Models with Accumulator
The accumulator is most often installed on the evaporator, near the firewall. (Click here for a typical photo)
Minimum Requirements
- Change or restore the accumulator.
- Drain the compressor oil and recharge with 134a compatible oil. (PAG or Ester Oil)
- Insure 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.
- Install thermostat if the system is not already equipped with one
- 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.