Tom M'Guinn

Does anyone have (or can anyone point me to) a step-by-step procedure for recharging the R12 in the 944, with pressure readings, etc. I've seen clarks-garage's write-up, and am looking for more if available.

Charlotte944

Try the Haynes TechBook 10425(1480): Automotive heating and Air conditioning
ISBN1 56392 071 9.

Although this book does not give Porsche specific pressures, R-12 is R-12, so the general information this book does provide will get you up and running.

83na944

This depends a lot on the model you have. I suggest you follow Cliff's advice and find a book on auto air conditioning. The system pressures depend on ambient temperatures, but for R12 try 20 on the low side and 200 on the high side. That ought to be safe, but probablly not optimal.

josephsc

I did this last year based on instructions obtained by searching on Rennlist and Pelican forums -- not that hard at all. The Griffiths website is also handy -- but it seems to be down at the moment. You do need to know how to
1) locate the low-pressure side of A/C
2) how to hotwire the A/C compressor using a battery cable
Let me know if you don't see it after searching -- I can do a little digging around once I get home.

Charlotte944

20 psi on the low side is (if memory serves) about 3 psi below the low pressure cut-out. I always shoot for about 29 psi on the low side. This is with the car open (windows down), fans on high, and RPM about 1200 or so.

If the compressor will not engage you can pull the wires off of the safety switch (which is located in front of the reciever/dryer) and jumper them together. Once you have the low side pressure above the cut-out you can reconnect the safety switch. Using this technique is a lot easier and safer than running a hot wire to the compressor clutch.

83na944

Yep 20 on the low side is low and 200 on the high side is low, too. But I figured if Tom is serious enough to get gauges, he'll figure how to use them with the charts and a thermometer. Otherwise, its really better to let someone else with the proper tools do this.

Tom M'Guinn

Serious I am. I got certified to buy the freon ($30). Bought 3 pounds of freon on e-bay ($40). Also have guages on the way ($40). It all adds up to less than half of what I paid last time I had a shop add freon (they all insist on evacuating and refilling the system).

josephsc

Did you get oil for the A/C system? Also available on eBay.

Tom M'Guinn

I need to read-up on that. My system has a slow freon leak. I was planning to just add freon, rather than evacuate and refill. When the freon leaks, does the oil leak too? I would have thought not the oil stays behind. No?

josephsc

I went through something similar a year and a half ago. I had a non-functional A/C system that I got diagnosed at a shop (local Firestone) who said there was a slow leak. I refilled it with R12 and a can of oil (w/R12) -- just in case. It's now running strong with no sign of weakening.

Someone on the old thread said there might be a deliberate slow leak to prevent over-pressure (though that seems wrong....)

83na944

Tom,

You need to read up on how to use the gauges. You can also use them to diagnose any problems.

Basically, you want to charge the system until the pressure in the low side is high enough that the evaporator doesn't freeze and the high side does not exceed spec. Low side should be about 30 psi. High side depends on ambient temperature in front of condensor, about 200 psi at 80F. You need a P-T chart. Follow the instructions with the gauge set.

Good Luck

944-LT1

hey try this site. http://www.escoinst.com/Section609.htm Click on the "download PDF training manual" this should cover everything possible.
You should really start with the leak test first. R-12 is a cfc and bad to vent out not to speak EXPENSIVE. Im 608 (commercial/residential) UNIVERSAL and 609 certified (automotive), and, found this site very helpfull to refresh.
Dont forget the 30 mph simulated air. Your gonna need a nice fan If you have any questions feel free to email me. Good luck Michael

Tom M'Guinn

Thanks for the link. I studied a very similar manual to get the 609 certificate, but found that it was light on practical information (heavy on regulatory/environmental information -- no surprise). My compressor leaks, and I will be replacing it over the next year (when I R&R the motor), but in the meantime, I thought I'd top it off. How do I know if I need more oil? Any other good links?

wheelblur

I'm going through the exact same thing ('87 944S). From what I've seen the low side is on the compressor directly. Is that the reason to bypass the switch in front of the dryer? Anyone with step x step would be greatly appreciated.

wilbur

944-LT1

You will need a manual for your car that shows location of the fittings high and low. I have one but cant find it right now.
Because most modern compressors no longer contain an oil sump or pump, proper refrigerant circulation is crucial since it holds small portions of oil as it moves throughout the A/C system. Passageways and internal pressures distribute this oil-laden refrigerant when it enters the compressor. Because the lubricant continuously flows throughout the system and does not stay in the compressor, any fault that allows the oil to escape from the refrigerant's grip or impedes the proper flow of refrigerant within the system will cause premature compressor failure.
A/C systems that operate at exceptionally low pressures are susceptible to premature compressor failure. Low pressures frequently occur during two operating conditions: a) cold weather in defrost mode, and b) systems functioning with low refrigerant charge. During these two conditions, insufficient low side pressure in the evaporator will not allow system lubricant to properly circulate with the refrigerant. During cold weather, thickening of the refrigerant oil only worsens this situation.
Many times, inadequate compressor lubrication is simply due to an insufficient quantity of refrigerant oil in the system. Refrigerant leaks, which take out oil with them, are a major cause of low refrigerant oil levels in A/C systems. Beware, when servicing a vehicle that has a low refrigerant charge, if you only top up a system with refrigerant you may be sending the vehicle back into service with an inadequate amount of refrigerant oil. Locating these leaks used to be simpler with R-12 because mineral oil leaves an oily, telltale residue that collects dust around leaking fittings. On the contrary, today's hygroscopic polyalkaline glycol (PAG) and polyester or ester (POE) oils associated with R-134a tend to dissipate and wash away dirt, leaving fittings solvent clean.
Most replacement compressors today are being shipped without the proper amount of oil recommended by the automotive manufacturer. When replacing a compressor, add half of the recommended oil to the compressor, and the other half to the new accumulator/receiver-drier, which should also be replaced at this time. Before operating the A/C system, always rotate the compressor shaft by hand with a spanner wrench a minimum of 10 times to clear any refrigerant oil from a cylinder. Remember, too much refrigerant oil is also detrimental to compressor life and A/C performance. Excess oil will sit in the condenser, slowly heating up, and act as a heat sink - preventing proper heat transfer. Symptoms of an oil overcharge include an A/C system that begins to perform properly with a standard 20 degrees Fahrenheit to 60 degrees Fahrenheit drop across the condenser inlet and outlet, then subsequently exhibits slowly rising head pressures and less than a 20 degrees Fahrenheit condenser inlet to outlet differential. This is due to the additional refrigerant oil sitting in the condenser and holding heat.
When a compressor fails, the condenser becomes the debris field. To prolong a replacement compressor's life, it is imperative that either a filter be installed to catch the debris, or the system be adequately flushed to remove it. Vehicle manufacturers and mobile A/C experts all have differing opinions on which method is best, or if a combination of the two is necessary. A concern with flushing relates to solvent residue that might be left behind, later hindering the lubrication properties of the refrigerant oil. One aftermarket supplier's A/C flush solvent, "Dura 141," has seen successful acceptance by the repair industry. It has a boiling point below 90 degrees Fahrenheit, so leaving residual solvent doesn't appear to be a problem. Charge properly, check for proper operation of low-pressure switches, and use the correct type and quantity of refrigerant oil. Keep in mind that a clean A/C system - clean both inside and out - provides you with the security of knowing you did the job right!