help with a/c compressor oil

mlang88 · 08-01-2009, 09:39 AM

im changing my compresssor i need to know how much oil to put in. the old compresssor was bone dry and the new compressor only had about 1oz of oil in it. should i put the 4oz the system uses? 1988 944 n/a

John_AZ · 08-01-2009, 01:13 PM

mattdavis11 and a couple of other Pelican members would have the information, but to fill in temporarily, I use the information from www.Griffiths.com. Here is a basic page and move down to the bottom. 4 to 6 oz is normal+-.

http://www.griffiths.com/achelp/achelp2.html

I am in the final steps of a conversion from R12 to R134a and my Nippondenso compressor was empty when I turned it upside down. I filled the compressor with about 2-3 oz of PAG (R134a) oil. I replaced the receiver dryer and put 1 oz in and 1 oz in the condensor. I did flush ALL the lines and pruchased a nearly new evaporator.

GL
John_AZ
1988 924S + 1987 924S

mattdavis11 · 08-02-2009, 02:20 PM

Hmm,no oil in the old compressor,. You should probably flush the lines, change the drier and start from scratch. 6-7 ounces is good for the whole system.

mlang88 · 08-05-2009, 11:49 AM

the944 says the whole system should only have 3.3 oz of oil for 1988. what will happen if there is say 4-5oz of oil in the system??

John_AZ · 08-05-2009, 12:15 PM

Quote:

Originally Posted by mlang88

the944 says the whole system should only have 3.3 oz of oil for 1988. what will happen if there is say 4-5oz of oil in the system??

Actually FRWilks site www.the944.com has the Porsche tech sheets and the amount of oil is 130ml+- 20ml =====150ml or so =========somewhere near 5 oz. Too much oil (I do not have that figure) could clog the lines or the expansion valve. http://www.the944.com/ac/page05.jpg

The amount of oil used is related to the items replaced.
Compressor-drained-refull with 2-3 oz
Dryer-add another 1 oz
Evaporator-add another 1 or 2 oz
Did you flush all the lines? add another 1 oz
Total 5-7 oz or so.

ALSO-according to matt----use only a little more than 2 cans of R134a if you convert or 3 cans of R12. R134a works best at about 80% charge.

GL
John_AZ

mlang88 · 08-05-2009, 02:05 PM

isnt that for converting to 134 im keeping it r12 i have a 50lb bottle that i have been sitting on. under the r12 tab on the site it says 85 1/2-88 as 3.3 total why would you use less oil with r12 when its the same system?

John_AZ · 08-05-2009, 03:54 PM

mlang88,

You are correct, the amount of oil for the R12 system is 3.3 oz. I do not know your answer. I did find other references to 5-7 oz in R-12 but cannot confirm.

I went back to the link I first posted:
http://www.griffiths.com/achelp/achelp2.html

AC OIL

What kind and how much: Compressors today are typically designed with aluminum pistons and cylinders. Rotary vane or scroll types may have steel components. The most common design you will encounter is a piston compressor. A few piston compressors may have steel cylinders with a teflon type sealing ring on the piston, though more commonly you will have aluminum pistons riding in aluminum cylinders, so good lubrication is important. R12 refrigerants require the use of a “mineral” type compressor oil. R134a refrigerant requires either PAG or Ester type oils. The PAG types come in various viscosities which are chosen by the compressor manufacturer. It is preferred with PAG types to remove or flush out as much of the residual R12 mineral oil prior to installing the PAG. Texaco and Castrol offer an Ester type that can mix with residual mineral oil, and this Ester type can be used with either R12 or R134a refrigerants. Vehicle designers typically will note the total ac system oil requirement on a vehicle or compressor sticker or in a manual, and measured in fluid ounces or cc’s. Too little oil will cause a compressor to lock up while too much oil will coat the evaporator and condenser walls reducing heat transfer. If you had to guess how much oil to use it would be wiser to have too much. The exact amount of oil to replenish will vary from vehicle to vehicle. With your typical replacement of a piston compressor the minimum oil replenishment averages 4 to 6 ounces. If you are replacing a drier, evaporator or condenser you should figure an additional ounce for each item replaced. In most cases a compressor supplier or the OEM vehicle mfg. will advise you how much of what type of oil is or is not in the replacement compressor. It is smarter to assume there is no oil in the compressor, and therefore you would attempt to empty the compressor and measure the oil (if any) that comes out of it before you install it in the car.

I did find more information on what happens if you use too much oil:

"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."

Again I hope someone who works in a shop can give the definitive answer.

GL
John_AZ

mattdavis11 · 07:38 PM

whoops, the late cars have a smaller system than the early. IIRC, 2.09lbs of R12 for an 88, but check some of my older posts about the capacity to be sure. Oil? It depends. The compressor and drier probably need 3.3oz if they are the only parts being replaced, but what about the rest of the system? You could probably put in 6 ounces of oil after you flush the lines and be just fine. Outside of that, you are going to guess, just like the last guy that checked the system and added 2 oz of oil. (that's a guess, I don't know if the system had been worked on previously, and you may not either, but it's pretty standard to add that amount)

I've never seen a system that holds as little as 3.3 ounces of oil. A honda civic holds four ounces and 1.4 lbs of refrigerant. Our compressors, as well as the entire system, are quite a bit larger.

mlang88 · 08-05-2009, 09:43 PM

thanks John & matt
so if the minimum is 110 (130+/-20) thats 3.71oz & the other states 3.3oz and i have 4.25oz
I should be safe right?

this is frustrating! the compressor was leaking out the front seal you can tell the PO tried to use a can of sealant to seal it. I put in the compressor and changed the dryer I had the compressor out for 2weeks while i did belts, oil cooler seals and a bunch of other stuff under the hood and a little oil game out of the lines just enough to make like a 50 cent spot on the garage floor. so im thinking if i leave the 4.25 oz I think i will be safe

Again thanks
Matt

John_AZ · 08-06-2009, 04:47 AM

Did you replace the front seal?
You did change the dryer and normally that would take an additional 1 oz of oil.
GL
John_AZ

mlang88 · 08-06-2009, 08:34 AM

It's a new compressor & dryer.