Nippondenso 10PA20C Compressor Rebuild pics


After re-doing all the o-rings in my A/C last summer, replacing the expansion valves, drier, and the relay in the head unit, the only things not up to snuff in my A/C were the two hoses that run to and from the compressor, the PITA pressure line that runs from the drier to expansion valve (R&Ríed now, see and the compressor itself. Well, at least one of these is leaking, as I lost my freon charge over the course of a few months. Time to fix that.

In addition to R&R'ing the pressure line and new compressor hoses, I decided to re-seal the compressor. To do this one needs a gasket kit, a and a shaft seal kit. The only special tools that the 10PA20C requires are some internal and external snap ring pliers (including a big one for the snap ring that holds the clutch coil to the housing) and a shaft seal protector- more on that in a bit.

I wasted about 2 weeks waiting for shaft seal kits convinced that Iíd gotten the wrong one (see
The shaft is about 13.5 mm in diameter, as was the ID of the old shaft seal. The new seals I got measured less than 11mm ID. Turns out this is ok- The carbon seal itself is deformable and can be Ďstretchedí over the compressor shaft. In order to properly install it, though, one needs a shaft seal protector. I ended up a MasterCool # 91319, from an outfit called Polar Bear ( for $15.

So- To rebuild the compressor:

Have the system evacuated unless youíre sure the system is empty- My charge from last year had completely leaked out again, hence the decision (after taking with Greg Brown about it) to replace both compressor hoses and re-seal the compressor.

A complete set of large combination wrenches from 17 to 32 mm, as well as a 1-1/16 and a 7/8Ē combo wrench are needed for all the combinations of fittings youíll find on the large diameter suction hose going to the compressor and the smaller pressure hose coming from it. There is only one fitting where you cannot counter hold, and that's a 19 mm fitting at the bottom of the down pipe from the drier to the condenser.

Removal of the compressor entails undoing the pressure and suction hoses at their fittings, then loosening the 10 and 13 mm nuts on the belt tensioner, and then undoing the two 17 mm bolts that hold the compressor to the mounting bracket. I pulled this bracket just to clean up the area:

Do yourself a favor and take lots of pictures of the orientation of the bracketry that hold the compressor and hoses to the block. Here are a few shots:



Passenger side:

Start by undoing the 10mm bolt that holds the clutch hub/cover plate. An oil filter wrench will keep the cover plate and compressor from turning.

Lift off the clutch hub, taking care to keep track of any shim washers that are between the clutch hub and the face of the compressor shaft- These set the Ďair gapí between the clutch hub and the clutch itself. Air gap spec on a 10PA20C is 0.3 to 0.6 mm. I had two shims of different thicknesses.

Hereís the front of the clutch:

The clutch/pulley assembly is held by a weird wavy-shaped snap-ring, and the clutch just pulls off easily.

Hereís the clutch/pulley bearing (Koyo DAC3052-3RR90, see the 'bearing madness thread for more on clutch bearings):

Then undo the Philips head screw that holds the clutch wire, and then remove the big snapring that holds the clutch coil to the compressor body. Itís indexed with a small pin. Sorry, no picture!

Youíre now staring at the face of the compressor, clean it up with some brake cleaner. Lots of oily greasy crap under the clutch coil. Perhaps my leak is/was from the front seal?

Remove the 5 case through-bolts with a 6 mm hex socket. My compressor was a rebuilt unit back in 1997, whoever did it used some sort of sealer on the threads. The gasket kit comes with five new brass washers for these bolts. Gently lift the compressor front plate off the shaft. On the inner face of the compressor front head is the shaft seal, held in with another snap ring:

Once the snapring is out the old shaft seal can be tapped out with a deep 10 or 11 mm socket:

Then remove the felt seal from the nose of the front head with a pick or somesuch:

To install the new seal, lube it up with compressor oil (Iím staying with R12 so I used ester oil) and install it by tapping it in (straight!) with a 19 or 21 mm socket.

The gasket kit includes three large (113mm?) o-rings to re-seal the case sections. No way in hell was I going to split the middle of the case, but I replaced the front and rear piece gaskets, lubed up first with compressor oil.

I cleaned up the faces of the case with brake cleaner, then installed the shaft seal protector over the shaft and oiled it well.

Now- this pic shows the old shaft seal at right, with an ID of 13.5 mm. The middle seal is ACKits.comís #21-34629, and probably would have worked. But I screwed it up installing and removing it from the front plate,so I reinstalled it briefly and used it for practice. It has been put on the shaft once and pulled off. The seal on the left is the seal I got from Polar bear inc, part # SS 767HNBR. At bottom is the shaft seal protector, with its beveled top, to ease the shaft seal over the nose of the shaft.

So with the new seal installed in the front plate, re-assembly is just a matter of oiling up the seal, putting the shaft seal protector over the shaft, and gently pushing the front plate and seal down onto and over the compressor shaft. Then remove the shaft seal protector, reinstall the felt seal (the kits donít come with a new one) and youíre all set:

I tried to install the case bolts but had some difficulty doing so Ėfelt like they were stripping. So I pulled the rear plate off the compressor to look at the threads. Ouch:

I ended up chasing the threads in the rear plate and running a die (M8 x 1.25mm) over the bolts to clean them up. Note the gray rubbery sealant crap in the recess in the tap:

Once these were done, I cleaned off the cutting oil then reassembled the compressor, torquing to a final value of 19 ft lbs. i didn't use any sealant on these bolts. I reinstalled the coil, clutch/pulley, and clutch hub, torquing the front hub bolt to 9 ft lbs.

Hereís measuring the air gap, at ~0.5 mm:

Last but not least I changed the gasket at the manifold plate, which is held on with 4 6 mm hex bolts. I added 6 oz of oil to the compressor before buttoning this up.
Ready to go back in:

I installed the compressor back in the car, replaced the drier, connected all the lines, and pulled a vacuum. The gauge hasnít budged in about 6 hours now- if itís still good in the morning Iíll pull a few more hours of vacuum on it and then charge it up.

This is an extract from Renn list bt Rob Edwards

As a side note if on A/C repairs you find any metal shavings inside the lines they should be flushed out and new receiver drier and expansion valve/s installed.
Finding metal shavings is a sign that you need a new compressor. Don't install a new compressor unless the lines have been cleaned

The paper towel holder- shaped compressor bracket that bolts to the block at four points has two lower M8 bolts that point straight up into the block, but the two upper mounting bolts run horizontally into the block. The anterior one is no problem, but the rearward one is located ABOVE the heat shield and is a PITA to install even with the compressor removed- you need a 13 mm socket on a 6" extension. I can't imagine getting to it with the compressor still attached, let alone torquing it properly.

That said, it can be a pain to get the compressor back up in there, when you put it into place you need to make sure that the bushing in the compressor mount isn't pushed too much towards the front of the car or you'll never get the mounting bosses on the compressor up and in between the flanges on the mount. The bushing can be pressed rearward with a channel locks. Also, the rubber portion of the compressor hoses both start out straight but require some pretty significant bends to line up with the condenser and the suction pipe.

EDIT: D'oh, I see what you mean. If you're just removing the compressor, yes, you could just drop the compressor itself off the swivel bracket (held by the 17mm bolts to the block mounting bracket) that it directly mounts too. In my case I had that whole area stripped anyway, as you need to remove the compressor and air pump to R&R the pressure line that runs to the expansion valve.

Stan- good point about the metal shavings, the one I show was threads from the rear plate. The rest of the inside of the compressor was nice n' clean. And despite having to chase all the threads, the bolts all torqued properly, so hopefully it'll behave.

The gauges on the vacuumed system didn't budge overnight, so I'll charge this afternoon.

Same basic process applies to the earlier compressors, like 6E171.

Just a few more pics from filling the system. a while back I splurged $20 and got my EPA 609 certification so I could buy R12 from Ebay. After pulling vacuum for a few hours this morning the vacuum was still at 30 mm Hg:

So- I closed both the low and high side valves, turned off the pump, then disconnected the high side hose. I connected up the yellow hose to my R12 tank, then cracked open the R12 and loosened the yellow hose at the manifold for 1-2 sec to fill the line with R12 then tightened it down. Then I zeroed the scale (got a good deal ($70) on Ebay last year, it's good to 100 lbs down to 1/10 oz or 2 grams.)

Here's the R12 tank before taring to zero, total weight = 32+ lbs:

With the system under vacuum, you need to jumper the pressure switch in order to get the compressor to kick in for filling:

{Oh, and you don't have to jumper the switch. Just open the low and high sides with the car off and let the freon get sucked in (since the system is under vacuum). Then shut off the high side, start the car and turn on the A/C.}

Then- start the car, turn on the A/C button with the fan on high (and crank the rear air fan and thremostat to full cold), and open the low pressure side valve. Since the low side connects to the suction line, the compressor will slowly pull freon into the system, at a rate of about 2 grams per second. I added a total of 1150g:

Then close the low side valve and the valve on the tank, disconnect the low side, and done!

The center vent temp is at 21oF by IR gun (I know they're not accurate, but it's cold....) So at least the compressor didn't immediately explode. I will report back when it does.

So if this works, I spent $20 for certification, $300 for R12 (but only used 2.5 lbs, so figure $25 worth), $200 for a vacuum pump, $70 for the scale, $12 for the seal, $20 for the compressor gaskets, $35 for a drier, $15 for the shaft seal protector and $20 for a ton of o-rings. That's about $400 for all the tools you need to re-do the system, assuming your compressor is rebuildable. Not bad considering a reman compressor is $500 alone. I don't even want to think what all this would've cost at the dealer in 1997.....


Some more (maybe too late...) thoughts:

-- Evacuate the hoses and the charging manifold all the way back to the bottle using the vacuum pump prior to charging. Use a spare hose to hook up the vacuum pump to the pressure safety switch port, the one you see there in the third picture. This is a little more thorough than trying to purge the lines with gas as you fumble with the yellow hose on a schraeder holding vacuum. Once vacuum is established for a while with all the charge plumbing attached, disconnect the pump while it's still running, and reinstall the switch before charging.

-- You can do the initial fill with liquid from the bottle. Engine is off. Fill to the high side so no liquid will get to the compressor. (must go forward through the expansion valve and evaporator, or backwards through the condenser before any gets to the compressor) Close the high-side valve as soon as liquid stops flowing. Let it set a bit to make sure all the liquid evaporates before you start the engine. Then finish the charging through the low side port in the normal fashion.

-- 21 degrees is pretty darn good, especially with a >80F ambient. Verify that the freeze switch is working if you plan any extended rides with AC on. Otherwise you'll be shutting the compressor down manually every once in a while to thaw out the evaporator box. You'll know when you need to do it when airflow is choked off by the ice block in there.
Bob Fuelleman


Porsche 928 AC-Compressor Original Denso 10PA20C

For Porsche 928 starting MY89
Type 5,0 GT/S4, and 5,4 GTS up to MY 1995
You can not exchange this compressor  with AC-Compressor 10 P15E MY 1988-1989 or AC-Compressor 6E 171 MY 1980 -1989