Over the road A/C repair - getting oil in the compressor?

[Brian Diehl]

I'll start this off with stating that I'm not an A/C guru and know only enough to be real dangerous.  With that said, the question I'm trying to solve is what is the easiest way to refill my compressor oil?  A couple of years ago my shaft seal failed.  I put a new shaft seal on and since there was still significant pressure in the crankcase I did not bleed down the system.  There was still enough oil in the crankcase that I felt comfortable running the A/C.  The A/C ran flawlessly for another two years.  Then, last summer I had no A/C and discovered the flexible high pressure outlet hose from the compressor had a pinhole leak in it.  So, I closed off the inlet and discharge valves and left it until this year.  Well, we are having a pretty hot year and I need to get this A/C working again.  I intend to pull the flexible hoses and get them replaced.  I also ordered a vacuum pump so I can evacuate the system.  Then I'll put my 24 lbs of R134A back in. 

However, the oil level is now at the bottom of the sight glasses and therefore I think I need to put a bit more oil in the compressor crankcase.  How should I go about doing this?  Currently the compressor is sealed off from the rest of the system and has whatever residual pressure in it that is left.  I can evacuate the compressor as well when I pump down the system.  Would vacuuming down the pressure in the crank case and then putting my gauge set intake hose in a container of oil and letting the vacuum pull the oil into the crank case work? 

Also, in regards to the oil, do I have to run straight Esther oil or can I run some of the Esther blends I've seen in Napa?

NOTE:  This system was converted over to R134 professionally many years back.

Thanks in advance for any helpful ideas you can share with me.

[baker4106]

You won't know how much oil is in the system until the compressor is working again.   Oil could be in the lines and evaporator and condensor.   Get the system working and check the sight glass for the oil level while it is running and add oil with a special pump through the low pressure side while it is running.   Can't answer about the proper oil.

[dbenck]

Brian, I have vaccum pumps and oil pumps for filling the system
you can borrow, in-place of buying, for the limited use you will need them.
I am just north of Somerset, WI

David P. Benck   

[Brian Diehl]

Thank you for the helpful replies.  David, thank you very much for the offer to help get the right amount of oil in the system.  I'll see how it goes back together and then catch up with you about the oil level in the compressor. 

I'm going to assume I should just go ahead and vacuum down the compressor with the lines once I have it back together so I can be sure the system is leak free.  This way I can also make sure and get the right amount of R134a (24 lbs.) back in the system upon refill.  Let me know if this is considered a waste of refrigerant or the proper course of action.

[dbenck]

Brian, as long as you know the system is sealed. I normally use a 100 to150 PSI nitrogen pressure
test...then draw a vacuum. It sucks when you find a leak with refrigerant in the system 

David

[Brian Diehl]

David,

Where do you get the fitting to go from a pressure regulator on the bottle of nitrogen to the acme fitting on the pressure gauge set?

Thanks.

[gus]

Anytime you open the system for any reason it must be evacuated before charging. You sure don't want any moisture in the system. Maybe Nitrogen will do the job since it pressurizes, never used it, but know it works well to save freon.

Air (moisture) is probably the single biggest problem I've found with auto AC systems.

134 does take different oil but can't remember the name right now. There is also a universal oil that works with both.

[dbenck]

Nitrogen is a dry inert gas which works well for this application.
It also absorbs moisture in the system while you leak check, making
the vacuum process work better/faster.
You need a regulator to mount on the bottle from tank pressure
(1500) PSI to 150 PSI..have one you can use. It might be easier
to have you bring it out and do it here...if no major leaks its takes
about 2 hrs ?? You have the refrigerant the rest is simple to check.
I have extra refrigerant here if you would need more to do the job.

David

[luvrbus]

I remember the Trane and Carrier compressors using straight mineral oil with the 134 has that changed ?

good luck

[Uglydog56]

When I rebuilt the A/C system on a non-bus vehicle and converted it to 134A, the tech was adamant that ester oil was the only good oil for a 134 system.

[Oonrahnjay]

When I rebuilt the A/C system on a non-bus vehicle and converted it to 134A, the tech was adamant that ester oil was the only good oil for a 134 system. 

     It's been a while and my memory is fuzzy.  Is that what they call PAO oil or is PAO the old spec stuff used for R-12?

[gus]

I had forgotten about those very high Nitrogen tank pressures since I used them years ago to inflate aircraft landing gear struts, they are to be used with great caution.

[Uglydog56]

PAG oil is supposed to be better at absorbing moisture and lubricating, but the viscosity has to be matched to your system, and it reacts harshly with contaminants.  Ester doesn't absorb as much moisture, but it is much more forgiving and universal in nature.  From the internet, Ester is preferred for retrofit systems (which mine was), and the proper PAG oil for a system originally charged with R134A.  I think mineral oil was used in the old R-12 stuff, but that's just a guess.

[RickB]

Brian, I highly recommend you coming up to David's for two reasons #1 you have to see both his buses and he is amazingly familiar with our bus AC systems. A great guy and a freakishly cool shop. #2 we live about 20 miles from him and we have 50 amp service at the house. We miss the Diehl family and could sure use a BBQ together. Let me know if you plan to make the trip.

[luvrbus]

Carrier did change oils I see they use POE now almost a gal for a dry system on a Prevost

good luck