R134A Conversion

From 1990 to 1993, the Z32's air conditioning system used the refrigerant called R12. Due to environmental concerns, the EPA declared "And low, thou shalt not sell vehicles with R12 A/C systems." So all the car manufacturers, Nissan included, made tweaks to their cars to use the more environmentally-friendly R134A.

This article explains how to convert an R12 system to R134A.
Credit to Piranha of ProjectZ32 for the original writeup.

Parts

• High side and low side adapters to convert your fittings from R12 to R134A.
• New receiver/dryer (should be replaced whenever the system is opened and exposed to the atmosphere).
• 2x 12 oz cans of pure 134A (no stop leak or oil)
• 4 oz of Ester oil if you opt to flush out all the old oil from the system.
• New o-rings (standard viton o-rings work great).
• AC Vacuum and Manifold Gauges (can rent from AutoZone).

Procedure

1. If the system is not already discharged, take the Z somewhere to a certified mechanic to have it discharged.
2. Remove receiver/drier (discard it).
   1. Remove the nose panel (2x 10mm bolts, 4x 10mm bolts for airbag-equipped Zs).
   2. Disconnect the two electrical connectors on the old receiver/drier bracket.
   3. Loosen the two A/C pipe fittings on the receiver/drier.
   4. Remove the 2x 10mm bolts securing the receiver/drier to the chassis.
   5. Remove the receiver/drier.
3. If replacing lines, disconnect all fittings and remove the old o-rings.
4. Flush each component to remove all mineral oil and debris (evaporator, condenser, lines). There is a drain plug on the underside of the compressor that can be removed to drain it's oil. Replace the same amount with PAG or Ester oil. I chose not to on mine because the replacement compressor I put on mine was already running 134A--unless you're replacing multiple major components (ie compressor and condenser), don't add more oil as there will already be plenty in the system.
5. Assemble all lines with new o-rings (lube with oil before assembly)
6. Last thing to install is the receiver/dryer (reverse of step 2).
7. Place system under vacuum for at least 1 hour. I rented the set up from AutoZone... will come with directions. This removes moisture and air from the system and will let you know if there are any leaks.
   • Vacuuming your system isn't to remove dust mites from the carpet. By creating a vacuum, the boiling/evaporating temperature of water is lowered, allowing any moisture in the system to evaporate and be removed by the vacuum pump.
   • This isn't a step that can be skipped. Not vacuuming will leave air in the system, which will lead to inadequate cooling and higher pressure. Old refrigerant, removed through vacuuming, also contains an oil that becomes corrosive when mixed with PAG oil in R134A.
8. With the vacuum pump turned off, leave the system under vacuum to ensure it holds strong vacuum for at least 20 minutes.
9. Charge system with 24 oz of 134A.
   1. Start the car and set the A/C to max cool (60 Degree/AUTO for auto climate control; slider to blue, fan speed on 4 and A/C on for manual climate control).
   2. Remove the dust cap from the low pressure fitting (the larger tube--it's near the firewall on TTs, and near the passenger headlight on NAs).
   3. Connect your A/C charging device (be it off-the-shelf sprayer or A/C machine), and begin charging. Follow the directions on the can to see if it's necessary to rotate/agitate the can while charging.
   4. After adding a few ounces (approx 7oz), the compressor should engage.
   5. Keep close eye on the pressure as you charge (it may be necessary to stop spraying momentarily to read it). Add refrigerant to meet the ideal pressure. Ideal pressure depends on the ambient temperature, refer to the chart below.
   6. Enjoy the long-lasting chill!

Ambient Temperature vs A/C System Pressures

These pressures should be measured with the A/C system running.

Ambient Air Temperature	Low-pressure Side	High-pressure Side
68°F	26.3 - 32.1 psi	149 - 181 psi
77°F	26.9 - 32.8 psi	162 - 199 psi
86°F	32.0 - 39.1 psi	195 - 237psi
95°F	39.1 - 47.6 psi	228 - 279psi
104°F	46 - 55 psi	263 - 320psi

Off-the-shelf A/C charging kits will only give you the low-side reading. Do not add refrigerant if the pressure is at or exceeding the recommended pressure. This will not make your A/C cool better, it will make something break.

Additional Notes & Upgrades

For those wishing to do a like-stock conversion, you can go a step further and replace the A/C Condenser with a later-model (R134A) type. These feature additional cooling fins to produce cooler output temps. Further, it may be necessary to replace the pressure relief valve (mounted on the high-pressure fitting at the A/C compressor) if it has blown. Some go so far to install R134A-designed compressors, but this shouldn't be necessary if your original is in working order and is properly evacuated.