Sanden SD7H15 Piston Rings

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Huff360
Posts: 2
Joined: Mon Jun 08, 2020 2:25 pm

Sanden SD7H15 Piston Rings

Postby Huff360 » Mon Jun 08, 2020 2:41 pm

Working on the AC system in a new to me 1995 Jaguar XJS with a Sanden SD7H15 compressor. I have replaced the condenser (due to a hole) and the drier (due to a broken desiccant bag) and the Expansion valve (just for good measure). I opened the compressor to inspect everything and found one piston to be missing the rings. I did not find any remnants of the rings anywhere in the system when flushing the hoses or the evaporator.

Before taking the system apart the compressor sounded fine and made good pressure on the high side. The cylinder walls look good and show no signs of scratches or damage. Is it possible that this was done on purpose or does this compressor need to be replaced?

IMG_20200607_085359.jpg
IMG_20200607_085359.jpg (101.01 KiB) Viewed 225 times
Dougflas
Posts: 299
Joined: Mon Apr 18, 2016 6:10 pm

Re: Sanden SD7H15 Piston Rings

Postby Dougflas » Mon Jun 08, 2020 3:22 pm

Hard to tell but replace the compressor. 1995 is over 20 years old.
Al9
Posts: 103
Joined: Tue Mar 10, 2020 3:26 am

Re: Sanden SD7H15 Piston Rings

Postby Al9 » Tue Jun 09, 2020 3:58 am

Definitely not done on purpose since efficiency decreases a lot once piston rings start missing. It's likely the reduced oil return condition due to low refrigerant charge that killed them. I have a spare evaporator removed from a car that was running a wobble plate Sanden compressor (with piston rings too), a parallel flow evaporator and a parallel flow condenser, and the evaporator inlet (together with the TXV high side outlet) was covered in black sooty oily stuff (even though the residual oil looked clean). The outlet was shiny clean, however; the contamination likely stopped inside the evaporator. In addition, more of this stuff came out dissolved in the old oil and flush while flushing the evaporator with an amateur setup. If the car had a parallel flow or serpentine condenser, the piston rings likely ended stuck inside it and then went about covering the rest of the system as fine powder, as in my case. Try cutting the old drier open and looking for them.

Good call replacing the TXV, as years go by its operating charge might slowly leak out and its spring might lose its original tension, ending in a TXV that no longer behaves like intended. I hope you used the OEM valve; automotive TXVs are nowadays finely tailor-made for each AC system and an aftermarket producer could possibly use a wrong operating charge, resulting in a TXV that feeds the evaporator in an inefficient way as heat loads change.
In my car, the OEM TXV even received an improved design at some point; the operating shaft has been encased in a 6mm thick black resin sheath (previously, it was a naked 1.5mm thick metal rod) and the body material has switched from a brass-looking material to pure aluminum. Since the thin metal rod is already an excellent low heat transfer rate anti-hunt design (my car has a variable displacement compressor reliant on stable TXV operation), the resin sheath is likely intended to suppress a torsional or bending force that was previously overlooked.

Replacing a 25 year old compressor is definitely a wise action that will pay in the long run.
Huff360
Posts: 2
Joined: Mon Jun 08, 2020 2:25 pm

Re: Sanden SD7H15 Piston Rings

Postby Huff360 » Tue Jun 09, 2020 12:13 pm

Thanks for the input guys. I've got a new one on the way.

As for the TXV, there aren't many Jaguar original ones left floating around! I did find one from Four Seasons that meets the original specs so hopefully it will perform as well as the original.

The old drier is a mess inside as the desiccant screen on the inlet side is broken. Luckily, the outlet side is still in tact and there aren't beads in the TXV or the evap.
Al9
Posts: 103
Joined: Tue Mar 10, 2020 3:26 am

Re: Sanden SD7H15 Piston Rings

Postby Al9 » Tue Jun 09, 2020 12:23 pm

Yes, just had a look on 4seasons and yours (4seasons 38822) looks like a genuine Egelhof product in the pics. I think it will be reliable.

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