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Chevy OBS, Chevy OBS AC hoses, Kwik AC hose kit, OBS AC hoses, Sanden AC compressor

Kwik Performance AC Installer’s Guide

A feature image for a blog that explains how to finish your Chevy OBS AC installation with proper amounts of PAG oil and R134 refrigerant

Wayne Powell |

How to button up your OBS AC upgrade — PAG oil and R134 amounts

Bolting on a new Kwik Performance serpentine system to your 1988-98 Chevy OBS truck is straightforward. Now we make it even easier with our custom, bolt-on AC hose kits that let you keep your factory evaporator and condenser.

So, what’s next? How do you make some cold air?

We get questions all the time about PAG oil and R134 refrigerant. Does the compressor come with oil installed? Do I need to add more to the rest of the system? How much refrigerant do I need to add?

Here are some practical rules of thumb for you DIY guys:

PAG Oil Requirements

Yes, you typically need to add PAG oil when installing new AC components. Here's the approach:

  • New compressor preparation: The Sanden AC compressors we sell come with PAG oil ready installed. So, none is needed there. But other new components will need additional lubrication.
  • Component oil requirements:
    • New accumulator/receiver-drier: 1-2 oz
    • New condenser: 1-2 oz
    • New evaporator: 2-3 oz
    • New hose lines: 1 oz per major line section. For our AC hose kits, that means about 2 oz.
    • Use these same guidelines for 1988-93 OBS trucks because you did flush the system of all the old R12 refrigerant and oil. Didn’t you?
  • Total system capacity: Most light trucks hold 6-10 oz of PAG oil total. When in doubt, start conservatively - it's easier to add more than to remove excess.
  • PAG viscosity: Use PAG 46 for most applications

When and How to Add PAG Oil

Add PAG oil during the installation process, NOT after the system is sealed and evacuated. Here's the proper sequence:

Timing in the Installation Process

  1. Before connecting refrigerant lines: Add oil to components as you install them
  2. After evacuation, before refrigerant: Final oil additions go in just before charging assuming you have a syringe or an oil injector tool that connects to the low-side pressure service port.
  3. Never add oil to a charged system: The system must be empty to properly distribute oil

How to Add PAG Oil

Method 1: Direct Component Addition (Preferred)

  • New compressor: None needed for new Sanden compressors
  • New accumulator/drier: Pour measured amount into inlet before installation
  • New condenser: Add through inlet fitting before connecting lines
  • New hoses: Add directly into hoses

Method 2: Through Service Ports (Secondary)

  • Remove Schrader valve cores from service ports
  • Use a syringe or oil injector tool
  • Add measured amounts through low-side port
  • Replace valve cores immediately
An illustration showing a PAG oil injection tool

Oil and dye injection tool

Method 3: Oil Injector Tools

  • Professional oil injector tools connect to service ports
  • Allow precise measurement and injection
  • Useful when you can't access components directly

Critical Installation Steps

  1. Use clean techniques: PAG oil attracts moisture rapidly - work quickly and keep containers sealed
  2. Distribute during evacuation: The vacuum process helps distribute oil throughout the system

Important Notes

  • PAG oil is hygroscopic: It absorbs moisture from air in minutes, so work quickly
  • Don't overfill: Excess oil reduces cooling efficiency and can damage compressor
  • System must be open: Oil won't flow properly through pressurized refrigerant
  • Turn compressor by hand: After adding oil but before starting, rotate compressor clutch several times to distribute oil internally

The key is adding oil while the system is open and accessible, then letting the evacuation and initial operation distribute it properly throughout the system.

Adding R134 Refrigerant

If you want to do this yourself, you’ll need two important tools:  

  • A vacuum pump
  • A set of AC gauges

How much refrigerant to add

Check the underhood label first - it's your best reference. If missing:

  • Typical capacities:
    • Pickups/SUVs: 28-40 oz
    • Suburbans with rear AC: 32-48 oz
  • Conservative approach: Start with 80% of estimated capacity, then add incrementally while monitoring pressures and cooling performance.
  • Pressure guidelines (engine running, 80°F ambient):
    • Low side: 25-35 psi
    • High side: 200-250 psi (varies significantly with temperature)

Key Tips for DIY if you have a vacuum pump and AC gauges

  1. Always evacuate the system for at least 30 minutes before charging
  2. Checks for leaks by watching your gauge set
  3. Use a refrigerant scale rather than relying on gauge pressures alone
  4. Add refrigerant slowly in small increments
  5. Monitor performance - proper cooling is more important than hitting exact capacity numbers
  6. Consider ambient temperature - pressures and performance vary significantly with outside temperature
  7. Taking your time and being methodical will get you good results.

The automated machines professionals use essentially follow these same principles but with precise measurement and automated controls. If you have any doubts about your capabilities, leave the charging process to the professionals.

More tech help available at:

info@kwikperf.com   or 417-955-1467