Kevin in Atlanta

I own an 87 S4 that was converted to 134a somewhere in its past. The car came to me with no Freon in the system. Today I had my shop evacuate the system to see if it held vacuum and if it did to charge it with 134a.

Well it held vacuum and my technician added 1.6 pounds of Freon using .85 of a R12 charge as a guide. I poked around here and I see that the 134A is actually 36 ounces. Is that also true for converted systems?

Now the front and rear ac is 75 degrees - way too warm. Am i under gassed?

Since the temp is the same front and rear I have ruled out mixing flaps.

When you evacuate does that that pull the oil out of the compressor and if it doesn't what happens if there is too much oil?

alabbasi

One of the problems with R134 is that it runs at higher pressure then R12. As a result, you use less volume to maintain the same pressure.

I would suggest switching back to R12 if you can. It's cheap and readily available these days.

ammonman

If they only charged 1.6lb you are under-charged. 16oz per pound *1.6 lb charge = 25.6 oz charge. If they reached target suction and discharge pressures with that charge weight then there is either a) excess oil in the system (likely from a "quickie' conversion) or there is air and/or moisture in the system. I recently did a complete re-seal and re-charge of my '90 with rear A/C using 134a and didn't use quite all of the factory specified 36oz of the 134a charge amount (more like 32oz.) I charged until the suction and discharge pressures along with vent temp was correct for ambient conditions per the charts in the WSM. I stopped before completely emptying the third 12 oz can of 134a.

Mike

76FJ55

In a mixed gas/liquid system which is what A/C systems are running the pressure is directly proportional to temperature. Varying the volume of Freon in the system has little effect on pressure. The pressure of the system can be determined by the vapor pressure of the liquid for the given temperature. R134a has a higher vapor pressure than R12 so the high side pressure for R134a will be higher than that on an R12 system even if the R134a system is under charged.

Ready availability and price of R12 seems debatable these days.

Eplebnista

For those of us still running R12, can you clue us in on where we can find the cheap and readily available substance you speak of? 12 ounce cans of R12 are going for about $30 each on flea bay and a lot of those sellers want you to show them an EPA cert...

rgs944

You can find it

rgs944

It's out there and the best way to purchase is in bulk. I purchased 30lbs a while back for $250 or something like that. That should do me for the next 10 years. Actually I could likely sell the remaining 25lbs I have for $300 so I guess you could say its not just cheap, it's practically free.

jleidel

For those of us who don't need 300 lbs of R12 laying around, convert over. It will only get tougher to find. I'm going to convert my 88' S4 to R134a. I have to rip everything apart anyway... might as well do it all at once.

j.kenzie@sbcglobal.net

I think he was talking about 30 lbs. But I completely agree that a good r134 conversion works great. I finished mine a few months ago and it is the coldest car I own. Much better than the half-assed conversion that I got with the car. I replaced or rebuilt everything except the evaporator and one hose. It is great.
Good luck,
Dave

dr bob

Charging to the gauges/temperatures and stopping as soon as you get there is not ideal. Simon's chart shows how the temp and pressure are related, but doesn't fully consider the actual volume of the system. R-134a does have slightly higher working pressure at most ambient conditions. In service, those pressures aren't significantly different until ambient exceeds about 95ºF, or you have a cooling fan failure.

In some perfect world, you'd be able to balance the pressures and flows in the system with the engine at its constant operating speed, heat load at a perfect value from the cabin, and ambient temp at some perfect design number. Then you'd charge the system to get the correct pressures, and keep adding refrigerant until the suction pressure started to go up. That's a sign that the evaporator is flooded and refrigerant is not completely evaporating, and that a little refrigebat needs to be removed. That perfect world doesn't exist for us though. Instead, if you charge like that, the flooded evaporator pushes liquid into the compressor suction and it grenades. So that "perfect" charge level is the one that ALWAYS has liquid condensed just at the outlet of the condenser, ALWAYS has the liquid completely evaporated just before the outlet of the evaporator. You can see when the charge level isn't enough or is too much, using the gauges. Finding the perfect spot in between those points is a crapshoot, hence the idea of charging by mass.

To the OP:

I'd add in the rest of the recommended charge, by weight. A shop may be timid about putting the full charge in, because they've seen or heard of systems that went boom! and they were on the hook for the fix. They should be able to confirm, with their gauges, that the suction-side pressures are still OK, and that the high-side pressures don't run away with the correct charge mass. With the car undercharged, you'll seldom see the capacity of the system used, since high-side pressure won't ever be high enough to continuously condense the refrigerant for the expansion valve. The suction side pressure will be low if the compressor is working, but you won't get ice-cold air though the vents.

dr bob

Mine's been on R-134a for 15 years now, and still freezes fingers on the steering wheel with 90º+ ambient temps here.

dprantl

If a properly converted R134a system can freeze me out of the car in 95 deg F ambient temps and over 80% humidity, why bother with R12 when it is so expensive and difficult to find? These days I play soccer at lunchtime in several times a week at a park. It gets really hot here, yet my car can get me cool within ~1 minute or less when I get in after the game. Increased A/C efficiency in this case is pointless. Listening to lots of conversion stories, it is no wonder why people think R134a is crap. Do the conversion right and you will not have a problem.

Porsche TSB89501 says to use 860g (30.34 oz) of R134a with no rear A/C and 1030g (36.33 oz) with rear A/C, so your system is undercharged. Since the system sounds like it was empty for a while, was the drier replaced?

It sounds like a vacuum pump was hooked up to your system, not an evacuation since it was empty. Vacuuming the system should not remove any refrigerant oil. However, you don't really know the actual refrigerant oil content in the system because you don't know the exact history of what happened to it. If it was my car, I would flush the evaporators and condenser, then empty the compressor of oil, then add the correct amount of ester oil (300 +/- 20ml for an '87S4). Insufficient refrigerant oil will not cause impaired cooling performance, but will eventually cause your compressor to die. Too much refrigerant oil will degrade cooling performance.

Dan
'91 928GT S/C 475hp/460lb.ft

The Forgotten On

If you are going to convert the system I would recommend using barrier lines instead of the stock lines because barrier hoses are designed for R134 and will not have refrigerant seep through them like the stock hose will. Also, if you are reviving an system that has not worked in years and find that your compressor went kaput (no affiliation) I would recommend the Griffiths kit as it comes with two barrier lines and a new more modern compressor designed for R134 for less than the price of a rebuilt stock compressor and lines. I'm using this kit in my car and hope to install it soon. I cant wait to move on from 2/60 A/C to a working system.

Kevin in Atlanta

This is where I think I am heading. I will likely have them evacuate the system next week so I can remove the condenser and clean it out while I replace the drier. I had great success when I converted my 86.5 to 134a and expect no less from the 87.

griffiths

The system has a leak, your ac tech should be addressing this (searching for the leak) as part of his procedure.

Pulling a vacuum and having it 'hold' is just a check for 'gross leaks'. Leaks should be checked using refrigerant dye/black light and a electronic sniffer.

The rule of thumb is to start off with 80-85% by weight of the original R12 weight noted for the model and year. And then adjust the final weight based upon a refrigerant P&T chart (pressures and temperatures chart) as noted in this thread.

You should be getting 'some' cooling affect with what was placed in the system; assuming all of the moisture and ambient air was properly evacuated. You could have an issue other components in the system, such as the compressor is not providing and adequate pressure differential (meaning you should have a reasonable difference between the low and high side pressures; here is where data you observe on the gauges comes into play, say you notice the outside air temp is 80F and you have a low side pressure of 30 and high side pressure of 200, the actual pressures will vary with the ambient air temp and the amount of refrigerant in the system). When a system is working properly to any extent you will notice a temperature difference at the inlet host to the expansion valve and the outlet pipe from the evaporator; the inlet hose to the valve will be warm to hot and the outlet hose from the evaporator will sweating and cold.

No. The only oil that will be removed from the system is any oil that is above the gravity line; meaning if the point where you are pulling the vacuum is below the service hose you will not pull out a significant amount of oil. Depending upon the make/model of car you might pull out a half an ounce or ounce of oil. Too little oil in a system and you will lock up the compressor. Too much oil in the system and the inside of the evaporator pipes become overloaded (coated) and the evaporator efficiency will be reduced; lack of sufficient heat transfer.

NEVER USE LEAK SEALANTS OR ANY ADDITIVES, JUST USE THE PROPER REFRIGERANT OIL AND EITHER 12 OR R134A.

We have converted hundreds of sharks to R134a during the past 20 years and when you do the work correctly they all blow cold.

PM if you need more assistance.