Hi Guys,

The never ending saga continues.

I'm thinking that rebuilding the rotary valve has the pneumatic system working now.  I have a vacuum pump and a new filter dryer.  I also borrowed a set of R12 gauges.  I also have 30 pounds of R12 (long story). Can anyone point me to a procedure specifically for charging ?  I know the system is flat and tight now (I pulled a vacuum and it held for two days). 

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the best way and easiest is with a refrigerant scale .

(this doesn't include changing oil in the compressor, removing old r134 ester oil from the system if it had been converted, i'm assuming you have flushed the system and replaced the oil, or that the system was never converted to R134a in its history.)

first, purge your gauges of air:
Make sure the hose fittings are tight on your gauge then attach your gauges.  Connect the yellow line to the vacuum pump, open both valves on the gauge manifold and turn on the vacuum pump.  Let it run for a minute after the vacuum reaches 30 in hg.  You can let it run another hour, if you like, to be sure old liquid is gone, but if you evacuated it completely already, you only need to take the air that is in the lines out.  
Close both valves tightly on the manifold and switch off the pump.  remove the yellow hose from the vacuum pump.  The manifold, lines, and system are now free of air that may have entered from the new hoses.

Second, set up the charging cylinder and purge the yellow charging hose:
Attach the yellow hose to the cylinder, open the valve on the cylinder, and turn the cylinder upside down on the refrigerant scale.  Loosen the hose fitting on the yellow line where it attaches to the manifold a little bit so that refrigerant comes out and then quickly retighten the hose when you see frost.  This will "prime" the charging hose with refrigerant and remove any air that may have entered the hose when attaching to the cylinder.    Zero the scale.

Third, charge the system with liquid refrigerant:

The car must not be running for this step!!! 

Make sure that:

  1. cylinder is inverted on the scale and that the scale reads zero.
  2. car is off.
  3. The red hose is attached to the discharge line (skinny one) and blue hose is attached to the suction line (fat one)
  4. You haven't repositioned the gauges or the scale, as this will affect the reading on the scale.  If you have, simply re-zero the scale and don't move the gauges again until charging is finished.
  5.  You check the charge amount for your car,  look in the service manual, remember that if it's a Fleetwood with a rear system, you use the specifications for your that system.  

open the red valve on the manifold gauges.  This will let liquid flow into the high side of the system.  Do not open the blue valve yet.  Watch the scale, and turn off the flow at the red valve when either it reaches the charge amount required or the scale reading stops changing.  

Wait for a minute or two with the valve closed for the low side to fill with refrigerant so there is refrigerant reaching the inlet of the compressor.  This normalizes pressure in both halves of the system and gives the liquid you just charged time to evaporate into gas somewhat to prevent the compressor from pumping liquid.

  If the scale reads the correct amount, you're done, you can close the cylinder valve and try it out!   If the scale stopped before reaching full charge, then continue by charging on the low side as follows:

Fourth (if necessary) Complete the charge through the low side port:

Being sure that the red valve is closed on the manifold and no liquid is flowing into the high side,  start the engine and turn on the ac system.  You will see the pressure on the low side (blue gauge) drop as the compressor pumps.  Note the pressure on the low side (blue) gauge after the pressure stops dropping.  Crack open the blue valve on the manifold just enough so that the low side pressure rises about ten or twenty PSI above the initial reading.  You don't want to open the valve too far or you will introduce liquid into the compressor and possibly bend the reeds.    You need just enough flow to allow the refrigerant to evaporate in the blue hose before reaching the charge port.    Close the blue manifold valve when the specified charge is reached, as measured by the scale.    Close the cylinder valve and remove the gauges then cap off the service ports immediately and check for leaks at the caps.   btw, I usually add an extra ounce of refrigerant to make up for what stays in the hoses after removal, but that's optional.  

That's it!  you're done charging the car.   Check the temp at the vent outlets and check that the pressure on the low side matches the setting specified by your POA/ STV set up, if applicable, and verify operation of the rest of the climate control system.

If you don't have access to a scale, you can charge the system using the low side and the sight glass, but this is more of a hit or miss approach really.    A fully charged system can show bubbles in the glass, and an undercharged system can have a clear glass sometimes, but if you have a clear glass you will likely have a near enough to accurate charge.

Special Notes for Charging on the Low Side or using replacement refrigerants:

If charging via the low side only, and if you're using R12 or R134a, you shouldn't turn the cylinder upside down.  This will make the charging time much longer, but completely eliminate the possibility of damaging the compressor while charging.  (im assuming here that your cylinder is new virgin gas.  if you're using a recycle cylinder, then use the valve marked 'vapor' or 'gas' for low side charging)    

If you are using a replacement refrigerant, such as 'hot shot', R409, etc, you must only ever charge these gases as a liquid since they are mixtures.  Always invert the cylinder when using these refrigerants.  Also, you shouldn't "top off" these refrigerant types if the system is leaking.  When using other refrigerant types, the system must be completely evacuated and recharged to maintain performance.  R12 and R134a are not mixtures, so they may be topped off in the event of a partially discharged system.


Really really nice info you posted on this AC subject
Good to know you are there to help out when the time comes To do your thing

Best regards




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