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2004 Nissan Pathfinder 3.5L V6 ~150k+ miles: A/C Work

Friend’s vehicle.

Mechanic had deemed the compressor as ‘bad’, so he bought an Ebay replacement for ~$150 (~6 oz of PAG-40 oil included), two cans of R134a, rented the vaccum pump and OEM gauge set from AutoZone, and is attempting the repair himself. He vacuumed the system for some amount of time (not sure how long) to remove moisture, then again pulled vacuum down to ~30 in Hg and it held for an hour or so. After that, he started charging the refrigerant. At 81 degrees ambient, the R134a chart says 40-55 psi on the low side, and 175-210 on the high side. System capacity is allegedly 1 pound, which would be a can and a half - and that’s what he’s charged to this point, but both gauge pressures are still not in range (40 on the low, 151-153 on the high), and the vent temp only gets down to 71 degrees. Should he charge, say, a half can more and see if that gets him there - even though he’s charged at least 1.5 cans so far, or is there something else he should be looking at?

BTW: he did not replace the filter/drier or condenser. He also said, on initial startup, the new compressor made a “terrible noise”, but stopped (maybe that’s typical of a new compressor on initial startup?).


Well, he added a little more refrigerant and noticed the compressor starting to cycle on and off. Is that pressure switch a High/Low switch (I always thought it was just a low switch)? Also noticed he had the outside air vent open. Closing that has allowed the vent temp to drop down to as low as 58, but that’s about it. Gauges are a little odd maybe … ambient is now up to 84, but now he’s below on the low side and above on the high side (39 and 300-ish). Is that high number on the high side an indication that he’s overcharged it? At 85 ambient, his high side should be 225-250 psi. If over-filled, can he just bleed some out?

Did your friend flush the system of the debris the old compressor left behind before installing the new compressor?

If not, that debris probably destroyed the new compressor. That was the terrible noise he heard.

Also, whenever a new compressor is installed, you always, always replace the filter/drier.


He said he did not flush the system. So the old compressor fails and discharges metallic debris into the lines and/or filter-drier/condenser components? How do you flush the system before installing the new/working compressor? Use some kind of a pump circulating what - waste refrigerant, or is there a special chemical you course through to flush it?

As you guys might remember, I’ve re-charged my cars’ systems a couple times over the years, but I’ve never replaced a compressor. So I did not get involved with his project. I felt like I didn’t have a firm grasp on all the steps involved and didn’t want to give him a false sense that I knew what I was doing just because I’d recharged a couple of systems 6 years ago. I did, however, mention the filter/drier replacement, because I ran across that in my notes when I revisited them to give him some pointers (like: DO NOT OPEN THE HIGH SIDE MANIFOLD VALVE!, and BLEED THE AIR OUT OF THE YELLOW HOSE).

So, if there was debris in the system, it circulated through the compressor, and if the compressor is still working, does that mean it won the battle and will survive, or is this going to be a slow kill? And what about opening the system again, re-flushing, re-vacuuming, and re-charging before running the compressor again?

This one of many flush kits on the market.

When a compressor fails, it’s called Black Death.

The new compressor will die pretty quickly.


Hmmm … makes me wonder about my 2011 Equinox. How do you know if your compressor has that Teflon “Black Death” in its future, and if you think you won’t be able to adequately flush the system, what are you supposed to do - replace a “working” compressor *before" it fails?

you can install an inline filter on the suction side, to prevent any remaining debris from literally getting sucked into the new compressor

This is in addition to flushing the system and replacing the receiver-drier

There might also be debris in the condenser. Just another thing to consider

I suspect your friend’s old ac compressor was making a terrible racket for quite some time, before it finally and catastrophically failed. That is a common, meaning that warning signs are ignored, until a component catastrophically fails


He said it was making a squeaking noise - like a bearing noise, that only occurred when the compressor ran.

He got 42 degree air today.

So you’re saying he should evacuate the system, flush, replace filter/drier, and add an inline filter? Something tells me he’s just going to ride this $147 EBay compressor into the ground and try it all again next season.