Recharging Empty A/c ?

[tmaki]

I just replace the A/C compressor on my '91 ES 250. Since the compressor won't run w/o pressure in the system, what is the proper procedure for recharging? ( I have vacuum pump, gauge set, etc. and know how to use them).

Pages AC-14 and AC-15 of the factory service manual describe the procedures for both vapor and liquid, but not a word about the dual pressure switch. I'm guessing with vacuum at specified level, refrigerant should be added in liquid form at the H/P side.

On the other hand, I made a jumper from the wiring harness of a donor car and the compressor runs with that in place. So, I could recharge at the L/P port with the compressor running.

Is there a preferred method? Or any else that should be considered?

Thanks!

T. Maki

[Toysrme]

I've never done one 100% empty, but you recharge from the low pressure side AFAIK.

You ALWAYS do it when it has some charge on the low pressure side.

Anyone else?

[tmaki]

I've never done one 100% empty, but you recharge from the low pressure side AFAIK.

You ALWAYS do it when it has some charge on the low pressure side.

Anyone else?

Just for the record, the manual does say on page AC-15, "5. Charge empty refrigeration system with refrigerant (liquid).

"This step is used to charge an empty system through the high pressure side with refrigerant in a liquid state."

It also says to never run the engine when charging this way.

There just seems to be a few details of the procedure that are unclear. And any reference to evacuation is three steps previous. Maybe some of those details are just understood.

Do you think it's reasonable to jumper the dual pressure switch to enable the compressor so as to charge from the l/p side? Or is it imperative to charge an empty system with liquid on the h/p side? There seems not to be a problem with compressor lubrication, as the compressor replacement procedure does not specify adding oil. Replacement procedures for all other major components have specific oil addition specs.

Continuing to wonder...

T. Maki

[mehullica]

Since you have a vacuum pump, pump the system down as low as you can. Then charge through the low side only, you will get in some charge due to the vacuum in the system and pressure of the charge cans. Once you have enough in to runs the compressor start it and let the a/c compressor pull in the rest of the charge at about 2000 rpm. Low side will take liquid or vapor, while charging without damage. Make sure you have added compressor oil to the system.

[wwest]

Since you have a vacuum pump, pump the system down as low as you can. Then charge through the low side only, you will get in some charge due to the vacuum in the system and pressure of the charge cans. Once you have enough in to runs the compressor start it and let the a/c compressor pull in the rest of the charge at about 2000 rpm. Low side will take liquid or vapor, while charging without damage. Make sure you have added compressor oil to the system.

Pardon me, but liquid into the "low" side will likely result in a failed compressor (once it is started) in relatively short order. Personally I would connect the refrigerant cannister to the low side, cannister top side up and below the fill valve, then wait for system pressure to equalize with the cannister pressure.

[mehullica]

Low side port on a es250 is well before the Evaporator which uses liquid R12 to "evaporate" and absorb heat. R12 liquid will not reach the compressor.

[wwest]

Low side port on a es250 is well before the Evaporator which uses liquid R12 to "evaporate" and absorb heat. R12 liquid will not reach the compressor.

The "low", suction side, of an A/C system begins "downstream" of the metering device into the evaporator and to the inlet side of the compressor. "High" side, begins at the output of the compressor. Compressed, high pressure "gas"flows to the condensor, is cooled to liquid form. Liquid refrigerant is typically beyond the condensor, to the dryer/reservior and now back to evaporator metering device.

[monarch]

I'd pump the system down as low as you can with the vacuum pump. Then charge R12 VAPOR through the low side only, with the can held upright (and engine shut off). Like mehullica says, "you will get in some charge due to the vacuum in the system and pressure of the charge cans." In addition, you can help this process along by immersing the can in a container of water that is about 110 degrees F. The hot water creates enough pressure in the cans to force R12 vapor into the system. (water temps of 120 degrees F or above could cause the cans to explode !!)

Once you have enough R12 vapor (approx. 1-2 cans) in the system while the engine is shut off , that will be enough to create sufficient system pressure to get the compressor to start up and run (if you turn the engine on). From that point on, set the interior AC controls for maximum cooling with the engine idling and let the a/c compressor pull in the rest of the charge out of the cans of R12 at about 2000 rpm. Charge enough to make the bubbles in the sight glass on the receiver-drier to dissappear. As mehullica says, make sure you have added compressor oil to the system.

On caveat: you should also replace the receiver-drier since the system likely become contaminated with moisture when it was totally empty of refrigerant (when old compressor was removed). Replacement driers come with the sight glass blacked out with paint. So if you replace the receiver-drier you can't use the sight glass anymore and will have to look up the refrigerant capacity for your model year ES250 and add only that amount. The factory manual also tells you how much new compressor oil is needed when you change the compressor and receiver-drier.

Still another caveat: if the original compressor suffered internal burn out due to loss of compressor oil, the resulting metal shards and debris could have circulated around and contaminated the system and possibly hasten destruction of the new compressor and the system expansion valve (the valve that meters refrigerant into the evaporator). But if just the magnetic clutch attached to the compressor seized / stopped working and burned up the rubber drive belt, then your old compressor itself really didn't burn up and cause any system contamination (because the magnetic clutch is an external device that has no contact with the refrigerant and compressor oil)

[wwest]

My own practice was to run the engine with the A/C on. The compressor will not actually run until enough refrigerant (as vapor) has entered the low side to raise the overall pressure above the "too low" limit switch.

Once the compressor starts to cycle it will defintely be an aid in "sucking" the refrigerant from the container. But my approach to how to tell when the system is full differs somewhat.

As Monarch says turn the system to max cold (be sure to over-ride the automatic mode switch to recirculate back into FRESH) and be sure the blower goes to max high. It's a good idea to open the windows or doors at this time so the cabin does not actually cool down.

If the evaporator air flow is too low (clogged filter, inlet blocked with leaves/debris?) then it will be possible for the evaporator exit air temperature sensor to sense/detect that the evaporator surface temperature is declining to a freezing level and that might result in the compressor being cycled off before the system is filled.

Once the system is filled, topped off, the compressor will begin to cycle on and off due to the refrigerant pressure on the high side reaching a maximum level.

If you're doing this outside in the open air above 75F you can stop here.

Otherwise my guess would be that when the compressor starts short-cycling, "on" time less than 5 seconds or so, you should stop the "fill"

As I have said before, as/when the compressor cycles "on" shortly thereafter you will see a transition in the sight glass from a total void, to a series of bubbles, than "solid" liquid flow, this latter looking EXACTLY the same as a total void.

Some modern day systems can restart the compressor before the liquid refrigerant in the sight glass is totally exhausted, used up, and in that case you NEVER see bubbles, only an EMPTY or FULL sight glass. Now the only way to tell that the system is topped off with refrigerant is by the fact the compressor is cycling on and off and the cabin cooling capacity is satisfactory.

Of course you can always FORCE the compressor OFF manually and watch for the liquid to bubble to EMPTY transistion and vice versa for compressor ON.