Carpokes

I did a how-to on changing my A/C compressor last summer and never posted it. I did it mostly for Crazy Eddie, because he needs a new compressor, but that’s still on his back burner. Since R12 has gotten stupid expensive on eBay, I also bit the bullet and finally converted to R134a. To keep is as cold as possible, I used all new compressor and receiver/dryer from Griffiths, along with their 134a-friendly parallel flow condenser. The bottom line is that the system works as advertised even with 134a. Vent temps get into the 30’s and 40’s even on the hottest California days.




Step 1: As always, I started by disconnecting and isolating the battery. I use my own 3D-printed battery isolator to keep the cable from hitting the battery terminal. I put it on Thingiverse for anyone who wants to print there own, or I can print one for any charter member who wants one (you pay shipping). I had the car on a lift. For the lift-impaired, you will need to get it up on jack-stands.
Step 2: Removed A/C belt and PS belt; removed PS and A/C turnbuckles.

Step 3. Removed black plastic batwing under front bumper cap.

Step 4. Normally, to be a responsible human, you'd need to evacuate the R12 in an eco-friendly way, i.e., using a shop with proper evacuation equipment. In my case, all the refrigerant had already leaked out the bad compressor, so there was nothing to evacuate. So...I just removed the two M8 bolts holding the two refrigerant lines onto the compressor (one bolt each) and pulled the lines off. Cleaned and bagged the bolts (M8 x 33 with washers – factory originals). O-rings were shot, but need to be replaced with new anyway (and they come with the Griffiths stuff.)

Step 6. Pulled single-wire spade connector out of clutch switch electrical connector. Very tight, really had to work it apart.

Step 7. Removed compressor-to-condenser hose so I could replace it with the Griffiths R134a version, along with the other hose on the condenser. Need to replace all o-rings. Also removed black foam piece that surrounds the two hoses where they attach to the condenser. The foam piece is just wedged over the hoses and pushed in place with no fasteners.

Step 8. Removed M10 x 50 (front) and M8 x 50 (rear) bolts (both 8.8 standard thread) holding compressor in place, and removed compressor. Came right out. Cleaned and bagged bolts (both with standard washers).

Step 9. Tried to “drain” oil from compressor but nothing came out. Oil gunked up around pulley shows pretty clear sign of leaky from seal. Removed four M8x20 Allen head bolts holding refrigerant hose “manifold” to compressor. This will need to be installed on the new compressor. Cleaned manifold of all gunk and oil, especially where seals go. Thought about blasting but didn’t want to risk getting grit in the system. Removed four old black o-rings between compressor and manifold, about 25mm OD, maybe 21mm I.D. Need to replace. Note, this manifold has a service port for recharging the system, even on my '86. On my '86, however, they had a service port on the refrigerant line up by the strut tower top, so I could put the r134a adapter port there, and don’t need to recharge at the compressor. Not sure about other cars. I’ve read “some” R134a conversion adapters are too big to fit in the limited space, so keep that in mind when shopping for 134a adapter ports.



And here's the compressor with the manifold removed.


Step 10. Removed MAF connector and MAF tube/filter to gain access to receiver/dryer in well behind the (USA) driver side headlight well. On a stock car, you'd just need to remove the black plastic air filter snorkel.


(continued next post)

Step 11. Removed hoses on receiver/drier to remove/replace it -- connections are 19mm, counter-held with 17mm; undid bracket with 8mm wrench. Note the “IN” side goes to the green sensor/switch toward the front of the car. Will need new o-rings here too. (All supplied by Griffiths if you get their parts.)
Step 12. Loosened receiver-drier bracket (8mm socket) and slid receiver-drier out of car. Removed bracket from frame to clean it and frame rail. New receiver-drier is 60mm diameter, whereas old/factory one (and bracket) is 67mm. Griffiths supplies a foam tape to fill the gap, which seemed a little sketchy to me. I fabricated aluminum spacers (look like crank bearings) so go around new receiver-drier and fill the gap.

I'm sure the foam tape would have been fine, but for how long?


Step 13. The caps on new receiver-drier were holding pressurized nitrogen inside to keep it dry, so left the caps on until the last minute. Idea is to keep air/moisture as much as possible until just before you charge it. Condenser was also pressure filled. Pull off those caps and reconnect as the last thing before pulling a vacuum on the system.

Step 14. Reinstalled receiver-drier bracket – now clean – and put new receiver drier in place with spacers but without hooking it up.


Step 15. Removed lower hose at bottom of condenser (19mm wrench, 17mm to hold fitting). Removed M6 nut securing that hose/line to side of radiator support. Removed two M6 bolts holding condenser mounts to car, with spring washers and fender washers. (Yes, two little bolt hold it in the car!) Wiggled condenser down and out of car. Rubber strips the condenser sits against are perished – need replacements. The upper front side of the condenser fins were all folded over by maybe ½”. Looks like the speedforce racing intercooler is a smidge too big and smashed the top of the condenser. The Griffiths condenser is a tiny bit shorter, so was able to adjust the intercooler just enough to fit the condenser without interference or altering anything.

"Air guide seals" between condenser and radiator were shot. Every little thing helps, so I had to track down new ones.

And here it is all cleaned up with the new seal, part number 94402511500. When I ordered the seal, I order "2", and for whatever reason they sent me a 10-12ft length of it. If you need any, let me know. I suspect it's the only supply outside of Germany.


After the lines are removed, the condenser is held in place with one M6 bolt on a rubber isolator, on each side.


Step 16. Removed the Schrader valves from both service ports on the driver inner fender and installed R134a conversion fittings (blue on low-side, thick hose). Installed to goodntite spec with open end wrenches after oiling the o-rings inside with a little oil from the new compressor. My calibrated arm was off, and I had to go back later and really crank them down to eliminate all leaks. The kit I bought came with a little tool for removing the Schrader valves -- they just screw out, but getting a grip on them without the tool is a challenge.


Step 17. Installed the refrigerant line manifold (elephant-face) from the old compressor onto the new compressor. Used the black o-rings (4) that came with the compressor (which were pre-oiled). Used the new Allen bolts that came with the compressor and torqued them to 18 ft lbs in a star pattern.


Step 18. Filled compressor with oil. Used the Auto 100 Ester oil Griffiths supplied. Can’t mix dissimilar oils, so relied on Griffiths to supply this universal donor oil. Made a dipstick and poured 5/8ths of the bottle into the compressor’s suction port (marked S) using a funnel. That gives me 5 oz of new oil (since the can holds 8). That was based on Griffiths saying to add 3 oz for new compressor, 1 for new condenser, 1 for new hoses, 1 for drier, but not more than 6 total. Since the evaporator and long line to firewall were not flushed, I opted to pull up short of the full 6 oz. There's no good way to measure the residual oil in the system, so you need to make an educated guess. Put plugs in port openings and put compressor back in car, finger tight, using the factory M10 and M8 bolts front and back.

Step 19. Re-connected to spade connector for the compressor clutch to the factory connector. It is a tight connector, so I had to shove it from the back of the terminal pin with a screwdriver to get it to seat all the way.

Step 20 . Installed new Griffiths high-side hose on compressor (the hose that goes to the condenser). Used o-ring supplied by Griffiths with a little ester oil on it. Cleaned off all the microencapsulation crud on factory bolt and used blue locktite on it. Torque it to 18.5 ft lbs. (Spec might be a tad higher, but with locktite it didn’t seem necessary – 18.5 was plenty snug.)

Step 21. Re-installed low-side hose on compressor (the one that goes to firewall). Used NOS Porsche o-ring I had “in stock” from last time I re-sealed the lines, with a little ester oil on it . The one Griffiths supplied was probably fine but the cross-sectional diameter was maybe a quarter to a half mm smaller. Cleaned microencapsulation crud off factory bolt and used blue locktite. Torqued bolt to 18.5 ft lbs. [In hindsight, probably should have used Griffiths o-ring since they are 134a friendly.]


Step 21. Put A/C-Alternator belt back on pulleys. Tensioned it to 9.5+ per manual on the 9201 tool (though maybe not a full additional turn, since that always feel "too" tight to me). Torqued M10 and M8 compressor mounting bolts to 33 and 17 ft lbs, respectively. Torqued turn buckle jam nuts to guttentite spec. Torqued turnbuckle mounting bolts, M10 and M8, to 33 and 17 ft lbs, respectively. Put yellow torque paint on bolts.

Step 22. Put power steering belt on pulleys. Tensioned it to spec (5mm of deflection). Torqued M8 pump mounting bolts to 17 ft lbs. Torqued turn buckle jam nuts to guttentite spec. Torqued turnbuckle mounting bolts to 17 ft lbs. Put yellow torque paint on bolts.

(continued next post)

Step 23. Test fit new Griffiths condenser. It is a wee bit shorter up top and “almost” fits under the SFR intercooler. Mulled hogging out the mount flange and just mounting it an 1/8” lower than stock, but instead removed the nose panel and adjusted the SFR intercooler up the few mm it needed for the condenser to clear underneath. Had to hog out the side-mounting holes for the SFR intercooler. Manage to jockey it just enough and get everything re-tightened. Put new duct tape on ducks in front of intercooler to better channel all air to it. With that, the condenser was able to slide up enough to mount in factory mounts without any modifications. Phew. Torqued the M6 mounting bolts in the rubber mounts to gootintite.
Griffiths consdenser is a "nice piece of kit" as Edd China would say.

Step 24. Unfortunately, the bracket holding lower condenser hose to the frame didn’t line up. Went back and forth with Griffiths, who learned of the issue when I flagged it and was great about it -- acknowledging it and vowing to address it. But I didn't want to wait, so ended up 3D-printing a flexible adapter mount. The original mount was a rubber isolator with studs, so wanted to offer similar vibration dampening, so I made it out of Ninjaflex rubber-like plastic, using heat-set brass threads. In truth, I'm sure the system would last a million miles without the bracket, but Porsche put a bracket on that hose, so I wanted to bolt it down.
My DIY adapter for the condenser house bracket.


Not the best picture, but this shows how the adapter bracket allows for the mis-aligned hose bracket to bolt up.

Step 25. Put new o-rings on the hoses to receiver/drier and tightened in place; reinstalled MAF and connectors. Pulled 29+Hg vacuum for 35+ minutes, using cheap Harbor Freight a/c vaccum pump.

Step 26. To recharge the system, I bit the bullet and got a big tank of R134a (the size of a propane tank), along with a scale from Summit Racing so I could track exactly how much I was adding. All in, I put in close to 31 oz. and the car is blowing plenty cold even on hot days. The instructions that came with the vacuum pump and gauge set from Harbor Freight were good. It's easy to get mixed up on which valves to open/close, etc. and their simple picture-based instruction cards were very helpful (better than the tools themselves actually.)

Step 27. Sniff tested with the electronic leak detector and didn’t find any leaks. Put R134a sticker on firewall and called it a day.

Great write up Tom
Cheers

This is great ….
Now when I get back I’ll have to loiter around your garage and finally install the compressor I bought 3 yrs ago !!

I put in close to 31 oz. and ...

Tom... a couple of questions... 1) do you remember your charge pressures? and 2) is your compressor cycling or is it just on all the time...Bruce

PS... I got all excited when I got outlet temps down low in the 30s. But then realized my thermometer was an antique and off by 10 degrees.

Tom --

Great write-up! I have a 928 but went trough a lot of the same effort converting it to R134a very soon after I got it. Car came with 18k on the odometer and stack of dealer service receipts. Most were for A/C system service it turned out. Car leaked from the factory it seemed.

Some thoughts and things I've learned particularly for people looking at this as a DIY effort, as well as for folks who might "just" be servicing their existing system:

-- The polyolester (POE) refrigerant oil is the one that's tolerant of some residual R12 mineral oil. Meanwhile, most replacement compressors ship with PAG oil in them. Griff gave you the right guidance and oil, but others out shopping in the free market for a compressor need to know that using the supplied oil in the new compressor will result in a failure. Denso recommends and ships PAG in their replacement compressors, so swap in the POE before installing it. Too much oil interferes with heat exchanger performance, so more than required is not a good thing.

-- The seal material used on the schraeder valves is particular to the oil/refrigerant. Replace all with new. In the 928 anyway, there are 2 charge/service ports on the compressor manifold (your Elephant Manifold), 1 under the pressure safety switch, and 1 under the pressure transducer that the 928 has for controlling cooling fans speed. The valves under the main service ports get removed as Tom notes, and the adapters are installed there. Leaving the old valves in those ports will lead to leaks as the new oil and the old rubber don't get along well. Get new port caps too, with the correct seal material in them.

-- ALL the o-rings in the system need to be swapped for the green HNBR material for the same reason. Porsche published a 'Parts & Technical Reference Catalog" in 1999, covering the A/C systems for 924, 944 and 928 cars, with blow-up diagrams of al the system pieces including the o-rings, with sizes and locations. Don't miss any.

-- The modern replacement expansion valves are better calibrated for R134a pressure/temperature profile. The same valves are used in other European cars of the period, so are amazingly inexpensive. Under $40 last time I looked in the aftermarket for my 928, maybe less for the 924/944 pieces.

-- Performance: Getting ALL the air out is essential to good system performance. Fugitive air in the system doesn't condense in the condenser or evaporate in the evaporator. It does take up heat transfer capacity in both, and also screws with compressor performance. The partial pressure of that air interferes with the temperatures of evaporation and condensation in the system. Bottom line, a very small amount of air will dramatically affect evaporator and vent temperatures.

-- More performance: The ideal operating condition for the system is at the lowest possible pressures where the system presents liquid refrigerant to the expansion valve(s). Those pressures vary with ambient conditions, heat transfer in the evaporator and condenser, and engine RPM's. Apparent performance in the evaporator is very subject to relative humidity, specifically the 'dew point' of the cabin air. The system will end up cooling the moisture in the air and condensing it, so evaporator temperature may not drop below the dew point of the cabin air unless there's additional capacity. Condensing moisture takes a LOT more energy than just cooling dry air.

-- If you can, find a receiver/dryer that has a sight glass in the top, so you can observe the state of the refrigerant as it exits the condenser and drier. Most 944 driers have these. I used a 944 drier in my 928 system conversion. Your target is a liquid flow with just a few vapor bubbles in it, with engine at 1500 to 2000 RPM. The state of charge for any particular condition may give you more or less bubbles, fugitive air in the system will always present bubbles there, etc. But 1750 RPM, fan on speed 2, is pretty close to normal drive condition. Charging by weight is a great starting point, and considers a range of ambient and operating conditions, but your target is lowest pressures with liquid at the expansion valve as witnessed at that sight glass. Adding more refrigerant raises pressures and therefore raises evaporation temperature, so less total cabin cooling is available. Somewhat counter-intuitive. Test/charge with any anti-freeze or low-temperature cut-out switches disabled.

So: best vacuum pump you can find please, with fresh pump oil in it. Leave it running on the system overnight if you can, so there's the best chance of evaporating and removing as much moisture and air as possible. Evacuate your charging manifold too all the way to your gas cylinder if you can. Purge the hoses (thinking yellow hose) with the refrigerant if you can't evacuate them. Do everything you can to avoid pushing air, even stray air in a charging hose, into the system.

With this level of care and proper charging, I see center vent temps of 19ºF cruising on a 90º+ day in my black converted 928 in our desert climates. It's easily enough to freeze fingers on the steering wheel. Fortunately there's an anti-freeze switch in the 928 that interrupts the compressor at 34º to keep the evaporator from icing closed. If you are seeing 40-50º vent temps at cruise conditions, the most common culprit is air on the system. In my experience anyway.

52Mhz -- My compressor does cycle on an off now. I can feel and hear it at idle when it goes on and off. I'll have to go back and look up what the pressures were. I remember the high side being slightly lower than all the charts suggested for the ambient temps, but the vents were plenty cold and I added plenty of R134a, so I left it. The Harbor Freight gauge set (and the vacuum pump for that matter) are not very confident inspiring. I am keeping my eyes open for a better version of both...

dr bob -- who knew you were such an a/c guru! Awesome post! Thank you!! I bought a new expansion valve, but it was such a pain to get to, and the old one was 'fine' so I got lazy and left it. Any recommendations for gauges and vacuum pumps?

Found my notes. It was 79F and about 50 humidity +/- and my pressures were about 40 and 165, according to the cheap-o HF gauge set. When I drove it around the neighborhood, the temps got below 35F at the vents, so I decided not to mess with good enough, particularly since I didn't trust the cheap-o gauges...

Tom --

Putting the new expansion valve in is easy since the o-rings need to be changed anyway. If you find you have leakage over time, part of the recovery effort might include replacing those o-rings you missed the first time. The POE oil will rot the black ones over time.

As far as gauges, the expensive ones work no better tan the cheap ones, so for a one-off effort the H-F gauge set is more than adequate. R12 gauges use a cylindrical seal where they mate with charge ports, and have a little metal depressor to open the schraeder valves in the charge ports. The seals deteriorate and the depressors fall out with age and oil exposure, and that's when having a name-brand set of hoses pays off; replacement hoses cost more than the cheap gauge sets, while seals are available for better hoses.

Vacuum pumps: I managed to find a laboratory-quality vacuum pump at an industrial auction a few decades ago now, and it's been doing the duty for me. Pulls to a few microns, way below what any of those little sliding-vane pumps will do. The sliding-vane pumps seem to be a common standard tool, but as you noted they pull to somewhere in the 29 INHG range. There are multi-stage versions, and while adding stages helps it's not perfect. For instance, the compressor shaft seal leaks if the system isn't run regularly. Now that my car is going through extended winter hibernation, and didn't get used much at all last year, the charge level was way low this summer. I put the pump on it for just half an hour, and charged it. Center vent temp is about 10º higher than it has been for the past 20+ years since the original R134a conversion. I'll likely reseal the compressor over the winter, then evacuate and refill next spring when we get our first warm days. For boiling moisture out of the system, the warmest day is the best day to do it.

Porsche offered a supplemental instruction for AC service as an addition beyond the model-specific instructions in the workshop manuals. I have a copy someplace. I'm generally not a fan of placing copyrighted material online for public consumption, but if I can find it I'm sure it would be OK for you to look at my book. The book has some generic tips for diagnostics, cleanliness (think surgically clean), assembly and evacuation/charging.

In my deep dark past, I took a refrigeration course at Standard Oil/Chevron to learn the basics for my own benefit. Then went on to study engineering. The fruits of that: If you happen to drive up 395 towards Mammoth Lakes, look east at the intersection of highway 203 when you turn uphill towards the village, and see one of my geothermal energy projects. It's a giant air conditioner running backwards. Heat from the ground boils isobutane across a (6x) gas expander, the mechanical opposite of a compressor. Big air-cooled condensers grab residual heat to bring it to liquid state again, and the liquid is then pumped through a heat exchanger to grab more energy from the hot water pumped out of the ground. There's another example just south of Reno, where highway 395 intersects highway 431 towards Lake Tahoe or Virginia City. You might pick up a theme here -- I like to live at ski areas. If it wasn't for the poverty, I would have been a ski bum. My little consulting gig now focuses on optimizing recovery of exhaust energy from gas turbines in power plants, boiling water and running steam turbines. I get to live near a ski area again, sans the poverty part thank goodness.