Pelican Technical Article:

1988 911 Nippondenso
A/C Compressor Rebuild

Rod Walter

[Click on Photo]

Figure 1:
Compressor removed, hoses wrapped

Figure 2:
Compressor overview

Figure 3:
Clutch drive plate removed

Figure 4:
Clutch pulley removed, exposing coil

Figure 5:
Pistons exposed with front compressor section off

Figure 6:
Front compressor section containing the shaft seal

Figure 7:
New seal kit, old seal removed

Figure 8:
Main case halves separated

     OK, 911 air conditioning wonít ever remind you of being above the Arctic Circle. And because of its design, the system has a lot of places in which leaks can develop. One of the more common points for a refrigerant leak is at the shaft seal of the compressor. You may notice some oil on the compressor mount or on the underside of the decklid in a line from left to right above the compressor. Many folks decide to buy a new compressor to solve this problem. But if youíve priced new or rebuilt A/C compressors you know that they can be quite expensive. However, with about $25 in parts, a three out of 10 skill level and 3 beers worth of time you can reseal your own compressor.

Tools you will need:

1.    A strap wrench or a large pair of channel lock pliers,
2.    A pair of snap-ring pliers,
3.    A set of deep metric sockets, especially 10mm, 11mm, 12mm, and 13mm,
4.    A 7/8Ē open-ended wrench,
5.    A 6mm hex key or socket,
6.    A phillips head screw driver, and
7.    A flat blade screw driver (for gentle prying).

Supplies and parts you will need:

1.    Lots of rags or paper towels,
2.    R-12 (Freon) or R134a compatible refrigerant oil (if you are using R134a make sure that the new oil is the same as what is already in the system),
3.    An compressor shaft seal kit, and
4.    A compressor o-ring gasket kit.

     The compressor that I rebuilt is a Nippondenso model 10P15C and the system is still using Freon (R-12) but make sure that you have the same compressor by looking at the model number on the small plate on the back of the compressor.

     I ordered both a shaft seal kit and a gasket set so that I would end up with a totally rebuilt compressor. You can, though, choose to replace only the shaft seal. The shaft seal kit has: 1) a new spring-loaded, carbon shaft seal, 2) a metal seal retaining ring/seat, 3) the o-ring for the seal seat/retainer, 4) a new circlip to hold the assembly in, and 5) new washers for the head bolts (these are the long bolts that hold the compressor sections together).

     The compressor gasket set contains mostly o-rings: 1) three large o-rings for resealing the case sections, 2) four small o-rings for resealing the suction and discharge fittings - where the shraeder (sp?) valves are located (you know, like the valves on a bicycle tire/inner tube), 3) one small o-ring for the shaft seal seat (a duplicate for the one in the shaft seal kit), and 4) five washers to use with the head bolts (again, duplicates for the ones in the shaft seal kit).

     Before beginning you should have any Freon thatís left removed from the system by an A/C shop - it shouldnít cost much and with Freon at $50+ per lb. they should give you some sort of credit for when you have it refilled. Discharging Freon (R-12) into the atmosphere contributes to the destruction of the earthís ozone layer and is prohibited by U.S. EPA regulations.

     Now you are ready for the rebuild. Begin by removing the compressor from the car and the clutch assembly from the compressor.

1.    Undo the two hoses from the compressor - the smaller fitting uses a 7/8Ē or 22mm wrench and the larger fitting uses a 1 and 1/16Ē or 27mm wrench but I carefully used a big pair of channel lock pliers since I didnít have an open-ended wrench that large. Secure plastic wrap with rubber bands around the hose fitting ends to prevent system contamination. Donít loose the o-rings on the hose fittings.  See Figure 1.

2.     Remove the three bolts that hold the compressor to its mounting plate, using a 13mm socket. Now you can tilt the compressor forward and take off the belt. Also disconnect the clutch wire.  See Figure 2.

3.     At the bench, kitchen table, or wherever (but probably not at the local tavern), remove the 12mm nut that is exposed at the nose of the compressor/clutch assembly. You need to hold the clutch drive plate in place to get the nut off or the assembly will just spin. This is the outermost piece of the clutch that has the rivets showing. Itís only about 3/8Ē or Ĺ ď thick and is separate from the pulley. Again, I carefully used a large pair of channel locks but the proper tool is a strap wrench. Once the nut and lock washer are off, the plate just pulls off. You can help it by carefully prying between the plate and the pulley assembly behind it. Watch for the spacers between the drive plate and the pulley and set them aside for reuse.  See Figure 3.

4.    The pulley is held in place with a 37 mm circlip. It doesnít come with the kit so try to remove it carefully enough that you can reuse it unless you have a good local source for such things. I donít. The pulley may be somewhat difficult to take off but you should not need anything like a gear puller. If you look inside the pulleyís shaft tube you can see the bearing that carries the pulley held in by a retaining spring. This may need to be replaced at some point. Mine did not require replacement.  See Figure 4.

5.     The ground for the clutch and a clip for the clutch wire are attached to the compressor by a phillips head screw. Remove it now. I had to slot the screw head with a Dremel tool and use a large flat-bladed screw driver because the screw was too tight.

6.     The magnetic coil is held on with a 46mm or so circlip. Remove it and, again, set it aside for reuse if possible. Pull the coil off. Notice that there is a locating pin on the compressor that mates with a hole in the coil for reinstallation. My coil had three holes but only one is in the right place.

7.    Take the woodruff key from the compressor shaft and set it aside so that you donít lose it.

     Now for the actual compressor stuff. The compressor consists of four sections: two end caps and two thicker middle sections with the pistons, cylinders and wobble plate (on the compressor shaft).

1.     Remove the five compressor head bolts using a 6mm hex socket or key. Each has a washer and you can discard them since you have new ones from either kit.

2.     If you are going to reseal the compressor take off the suction and discharge fittings, noting their placement. They will go on the wrong way (ask me how I know) and if you do happen to get them on wrong during reassembly just remove and switch them. Donít remove these if you are not going to reseal the case.

3.    Once the head bolts and the suction and discharge fittings are removed the case sections will just split apart under hand pressure. To replace the shaft seal only, pull off just the front section of the compressor. You will be able to see the tops of the compressor pistons and one of the large o-rings for the case.  See Figure 5.

4.    The front piece of the compressor with the ďnoseĒ is where the shaft seal is located. Look inside the nose, find the felt seal and its brass retainer and remove them. They are to be reused.

5.    Remove the circlip from inside the nose. You do have a replacement for this so donít worry about ruining it.  See Figure 6.

6.    From the inside (compressor side) of the nose drive out the seal and its retaining ring with a 10mm or 11mm deep socket and a hammer. Go carefully so that the seal and ring donít ďcockĒ in the housing. You will destroy the old seal - when you see pieces of carbon donít worry about it. The retaining ring is held in place with a friction fit using an o-ring. It may help you to remove the seal if you lubricate the nose with some of your refrigerant oil. The seal itself sits loosely inside the shaft housing (nose); itís not pressed against the sides.

7.    Once the seal is out, clean the shaft housing so that you donít have bits of carbon in there.  See Figure 7.

8.    Install the new seal. The spring-loaded carbon assembly drops in first, the carbon facing out and the spring toward the rest of the compressor. You should avoid touching the carbon itself. Now, you may notice that the retaining ring is different than the one you removed. One side of the new ring has a flat surface - put the retainer in with this flat surface facing the carbon seal after lubricating the new o-ring with refrigerant oil. Now here I made a judgement call. The new retainer will not take up the whole space between the seal and the circlip that you removed . I drove the retainer (with a 13mm deep socket) to a point just below the groove for the circlip. If you study the assembly, the actual seal is formed by the carbon piece pressed against the retainerís flat surface and the circlip just prevents the pieces from working their way out along the shaft. When you place the compressor nose back on the compressor the seal will be spring loaded against the retainer creating the seal. I suppose that you could drive the retainer all the way to the seal but I chose not to.

9.    Install the new circlip in its groove.

10.    Allow as much of the old refrigerant oil to drip out of the compressor as you can and put 2 oz. of new oil in the compressor. Where you add it doesnít matter - it just circulates throughout and is carried by the refrigerant around the system.

11.    If you are not resealing the case you are finished and can begin reassembly. When replacing the compressor nose piece be careful to avoid nicking the carbon - just put the shaft through the seal as straight as you can.

12.    If you do reseal the case simply separate the sections, replace the large o-rings and put it back together. All of the components are constructed in such a way that proper reassembly is made obvious with pin locations and non-symmetrical parts. Also replace the four o-rings at the hose fittings. Hint: separate the two large case sections, replace that o-ring (lubricate with refrigerant oil), replace the four hose fitting o-rings, put the fittings back on and only then remove the rearmost case section to replace its o-ring. This will make sure that the pistons and wobble plate donít wander out of the compressor while you are working. They are a royal PITA to put back together.  See Figure 8.

13.    Using the new washers, reinstall the five compressor head bolts. If not yet reinstalled, replace the hose fittings.

14.    Replace the clutch assembly. Make certain that you reinstall the spacers between the pulley and the clutch drive plate.

15.    Remount the compressor, hook up the clutch wire and reattach the hoses, lubricating (and replacing, if necessary) the hose o-rings.

16.    Take the car to an A/C shop and have it refilled. To be secure and happy you may want the technician to put a leak detector near the compressor shaft to check your work.

17.    Youíre done!

If you use this article to rebuild your compressor and find that Iíve forgotten something or have been unclear, please e-mail me with feedback. Good luck!

Rod Walter
PCA Lincoln Trail Region