AC Pressure Charts / Reading Gauges (R12 and Retrofit)

[Ron]

DeLorean Worhshop Manual (N:09:01)-
Pressure Check Data - Heating and Fault Diagnosis

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Note:

Ambient Temp Measured ~2 Ft in front of Condenser
Engine temp must me normal -- Use a Box fan if needed.
Pressures to be taken when clutch cycles out!!!



Reading Gauges
(Taken from several sources, does not apply to expansion valve systems!):

Low side: HIGH -- High side: HIGH
(Warm Duct Temp):
• Too much refrigerant.
• Poor condenser airflow.
(Some cool):
• Non-condensable gases (air) in the system.
• Moisture in the system.


Low side: LOW -- High side: LOW
• Not enough refrigerant.
• Restriction in screen (High Side Port)
• Compressor problem.

Low side: LOW -- High side: HIGH
• Plugged orifice tube*
• Restriction in screen (receiver dryer)


Low side: HIGH -- High side: LOW
• Compressor valve problem.
• Missing/damaged orifice tube*


Low side: Vacuum -- High side: HIGH
• Low side restriction
• Plugged orifice tube*
• Moisture in the system

* Variable Orifice Tube Adjustment

[Ron]

The following is from a FREEZE 12 (c) Tech Tip.

When converting R-12 A/C systems over to Johnsen’s Freeze 12, the amount of Freeze 12 to be charged is approximately 10% less than the amount of the original R-12 charge. However, in many cases the original R-12 charge is not known due to missing service labels or custom designed A/C systems. In addition, an accurate method of recharging 10% less Freeze 12 (like a digital scale) may not be available. As a solution, based on the field conversions of thousands of R-12 A/C systems to Freeze 12, an alternative method of recharging is available:

Set the engine at 1500 RPM until the vehicle reaches normal operating temperatures. Determine the temperature (using a calibrated thermometer) approximately 2 foot in front of the condenser.
Add 40° to the temperature observed.
Using a R-12 pressure/temperature chart, locate the temperature calculated in Step 2 and read across to the associated pressure. This is the target high side pressure in the system being converted.
Slowly, recharge the system being serviced with Freeze 12 until the high side pressure is approximately equal to the target pressure found on the R-12 pressure / temperature chart.


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Example: Holding a calibrated thermometer approximately 2 foot in front of a condenser, a technician observes a temperature of 80°. Add 80° + 40° = 120°. On a R-12 pressure/temperature chart, 120° corresponds to approximately 157 PSI Slowly, charge the A/C system with Freeze 12 until the high side pressure reaches approximately 157 PSI.

(Applies to some other refrigerants calling for a 10% reduction in charge.)

[cdrusn]

This is a highly professional and excellent thread. It gives great troubleshooting ideas. I have converted several cars including my Delorean to R134 in order to have easy access to freon from the local parts store. The simple way is to buy the low side port from the local parts store and a cheap gage set from Harbor Freight. Put the low side port onto the R12 fitting, you have now converted your system over to R134. Buy the can of R134 that comes with the PAG oil inside the can. Hook up the low side (blue) line to the new R134 fitting, start the car, put the a/c on full, open the valve on the can and let it enter the system. Your compressor should begin to draw in the clutch off and on until the system reaches about 35 lbs. at which time the system should be quite cold. At some point but not immediately you will have to change all of the 'O' rings to the newer green rings also available in a complete kit from Harbor Freight. You will periodically have to recharge the system but no more than twice a year. If you have to do it more often you have a leak somewhere and you have to decide if it is cheaper to allow it to leak or find the leak and fix it. :cool1: