AC compressor replacement help needed - PeachParts Mercedes-Benz Forum

sixto · #1 02-20-2010, 04:03 PM

I'm replacing the AC compressor of my 87 300D because the compressor leaks refrigerant. The compressor still works, a trusted shop don't think it sent shrapnel through the system. My plan thus is to replace the compressor and have the system recharged with R-12.

There's a list of items I can change (expansion valve, drier, etc.) but I'd like to know what I should change.

Questions:

1) A shop I trust says there's no need to replace the drier if the system is clean and hasn't been exposed to moisture. What are the pros and cons other than cost?

2) Ditto the expansion valve?

3) Should I replace other system seals, at least the ones in the engine bay?

4) Which are better - green o-rings or black o-rings?

5) There is grime around the low pressure Schrader valve. I clean the area and it's grimy again by the next oil change. Should I replace the Schrader valve?

Thanks,
Sixto
87 300D

Matt L · #2 02-20-2010, 04:12 PM

If the system is evacuated and then flooded with dry gas (such as nitrogen), you won't be adding much water to the dryer and reusing it is almost certainly fine, if the work is done quickly. But if you're taking it apart and replacing any other system seals, replace both the dryer and TXV.

If you're sticking with R12, you can use green or black o-rings. Be sure to use the appropriate lubricant for R12.

The service fitting cap should seal the low pressure port. You can replace the valve core, but also ensure that your cap seal is in good shape.

Jeremy5848 · #3 02-20-2010, 06:36 PM

I don't know the parts costs involved, but once the system is evacuated of Freon and you're doing the work yourself, I would replace everything I could easily access (i.e., NOT the evaporator) except the condenser. Make sure the condenser fins are clean, though.

sixto · #4 02-20-2010, 07:55 PM

That's another angle to my question - should I replace a couple hundred dollars worth of hoses? If not, should I touch fittings that have been happy for 23 years to replace o-rings?

Thanks,
Sixto
87 300D

oldiesel · #5 02-20-2010, 08:46 PM

If your system is still holding pressure i would not go taking apart connections that are NOT leaking on the chance that they will not leak when reassembled with new o rings these are old cars and disturbing things can open a big can of worms.If the hoses look rotten a good A/C shop can replace the hose part and reuse the pipes for small money compared to MB prices. Don

Hit Man X · #6 02-20-2010, 09:07 PM

The dryer and exp valve are so inexpensive, why not?

I have also been taught that whenever the system is opened, you replace the accumulator/dryer.

Yes, replace the o-rings. I am sure the hoses are fine.

Schrader valves are also inexpensive, I would replace.

Test the temp sender on the head, if questionable replace. I would get the red one as it kicks the aux fan on soonest.

I would consider a flush so you can have the correct amount of oil in the system upon compressor install.

leathermang · #7 02-21-2010, 01:04 AM

You should not be trusting that shop..
Everyone who knows anything about AC systems knows that if you open the system at all you must replace the receiver dryer... there is no question about that... go to another shop for the rest of your AC work.

Read Hit man X's post and follow it closely... those are all industry standard safe answers...
except that assumption about the hoses... that will be determined by your pressure test with nitrogen and R22 before you do your vacuum immediately before filling your system ...
The part about flushing with regards to the amount of oil in the system is very important.. that is the only way you can know that you have the proper amount ..and that it is clean.... and you can not just add... because too much oil is very bad also...