A/C Servicing Questions

[Robert Coats]

My car is a '91 C4, converted from R12 to R134a. It has a minor leak, as each spring I have to add 1-2 cans of R134.

This year, I checked some of the fittings and found a fair amount of black oily film around the receiver/dryer. Since it appears to be the original, 15-year old part, I went ahead and put in a new one. The o-rings looked okay.

Now, I have a vacuum pump on order...what is the correct procedure next?

(1) Connect vacuum pump and vacuum system for a few hours. Check gauges, and see if system holds vacuum okay.
(2) Disconnect vacuum pump. Run A/C system. Add R134 to specs (I think it's about 2.something pounds on the sticker).

Is that all there is?

Will the compressor engage and start sucking if the yellow supply line is open to a full can of R134?

How about oil? I know the R134 has oil. I also heard the oil stays in the system unless you blow/flush it out. Vacuuming will not extract the oil? I do not want to seize the compressor.

Is it necessary to flush the system? I have compressed air, but don't know the proper procedure.

What else should I do to correctly service/charge the system?

-Robert
Hotlanta

[rfuerst911sc]

If you are saying you replaced the receiver drier but used the existing orings on the hoses I think you will be in trouble as it probably was the orings that were leaking. You can purchase the green colored orings at local auto parts stores for less than $5.00. Once you have done that and if you feel that you haven't lost much oil then yes go ahead and pull a vacuum, I would recommend about 2 hours or so. Then turn off the pump and let the car sit overnight,if the next day your gauges indicate no leaks then go ahead and throw in 1 can of refrigerant the system will suck it right in. That will be enough of a charge for the compressor to kick on and then you can continue to add until you are up to the required amount.In my opinion you do not have to flush the system because you did not have a catastrophic failure you just replace one component.Make sure you know the high side from the low side,if you get that wrong bad things can happen to you! Good luck.

[Robert Coats]

rfuest911sc, that is exactly the help I needed. Thanks so much sir!

[rfuerst911sc]

That's what this community is about.If you have any further questions feel free to PM me.

[Jim Sims]

A/C compressors must have oil to operate properly and not wear out prematurely. The oil must be of the proper type and amount. The oil in an automotive A/C system continually leaves the compressor and must be circulated back by the flow of refrigerant. For this to happen, it must be compatible and miscible with the refrigerant being used. The proper oil for use with R134a is either PAG (Polyalkylene Glycol) or POE (ester); both of these types readily evaporate at a leak site so what you are likely seeing is the original mineral oil left over from the R-12 days. Receiver/driers should be left sealed and installed right before evacuating the system; one of their functions is to continually remove water from the system after it is evacuated. Installing it before and letting it sit exposed to an unevacuated system uses up some of the functionality of the contained dessicant. Proper evacuation requires pumping down below 40 microns for at least three hours; venturi type vacuum pumps run off compressed air are typically not adequate nor are many single stage pumps or even two stage pumps if the pump oil is old and saturated with water. It is helpful to have the car sitting in the hot sun (mobilizes the water so it can be pumped out) while pumping the A/C system down.

The car being discussed should have the compressor removed; drained of oil and the oil replaced with the proper amount of POE oil. All of the o-rings should be replaced with the R-134a compatible type (green or blue color). There are likely 10 o-rings: two at each condenser; two at the evaporator; two at the compressor and two at the receiver/drier. This is a convient time to flush the condensers (aerosol cans of flushant with appropriate nozzle fittings are available to do this) of any remaining mineral oil and drain the low spots at fittings in the refigerant lines of mineral oil. Evacuate the system and then leak check. If tight, then charge using a set of refrigeration gages and thermometers to monitor pressure and temperatures. Sight glass method doesn't work with R-134a. Charge only through the suction side of the compressor; if you don't know what this means obtain knowledgeable assistance. Automotive A/C systems can maim and kill you. Back hatch down (so engine fan will pull air over rear condenser) while charging. Wear safety goggles and do all charging outdoors.

Jim

[Robert Coats]

Originally posted by Jim Sims
The proper oil for use with R134a is either PAG (Polyalkylene Glycol) or POE (ester)

Doesn't the can of R134A have oil mixed in with it?

All of the o-rings should be replaced with the R-134a compatible type (green or blue color).

When I swapped out the receiver/dryer, the two fittings had black o-rings; are these OEM (R-12) types? Might explain why I've needed to recharge the system each spring.

[Jim Sims]

"Doesn't the can of R134A have oil mixed in with it?"

Not necessarily: standard cans only have refrigerant but you can get cans containing the correct oil (use only POE or ester oil in converted systems) and a small amount of refrigerant. One can also get cans of refrigerant containing sealant or UV dye; sealant is a real bad idea and the UV dye is only slightly better. Having sealant and or dye in your system can mean a professional shop will refuse to work on it in the future. Manyof these shops now have detectors that check for this type of stuff plus the non-standard refrigerant types.

Using the cans with oil and refrigerant together is convient but one really doesn't know how much oil is in the system; excessive oil coats the interior surfaces of the heat exchange surfaces (condensers and evaporators) and diminishes performance. I will conjecture a major reason for reduced performance of converted R134a systems is excessive oil from poorly done conversions.

Black o-rings (made with older versions of Nitrile rubber compounds?) are likely from the R-12 system days and the oils used with R-134a may attack it. Reusing o-rings, even of the correct compound is unwise; new ones are so cheap why risk a leak and having to do the job over?