Auto Service World
Feature   April 2, 2003   by Tom Brown and Jim Anderton

Too Much of A Good Thing

AC expert Tom Brown reveals that some unusual chemistry and excessive lubrication in a dealer-installed Honda system killed two compressors in a row in an otherwise innocent system.

The customer did everything right. The Honda Civic with dealer-installed R12 Air needed a retrofit and a replacement for the tired Matsushita compressor. The Retrofit was properly done, with through system flushing, nitrogen purging and a fresh receiver dryer. Dye, sealant and a performance enhancing additive were installed for good measure.

The system ran great for a week then, even though the compressor spun just fine, there was no cold air.

Tom Brown, Professor of Automotive Air Conditioning at Toronto’s Centennial College and Director of ACExperts, an Automotive AC troubleshooting and training service, cracked the hot Honda.

Brown was, and is, unequivocal about the procedure. “Always use the checklist first” he declares, referring to the standard guides like the one SPI publishes under the firm’s Certi-Cool banner. Brown held up his hand and stated, “This is diagnostic tool number one”, after which he began with simple function checks of the dashboard controls, followed by a look for compressor clutch engagement. It spun, so hands were run along the lines. Not hot, warm or cool where it should be. A pressure test revealed 70 psi on both High and Low sides with the compressor engaged. Since the system had the dye pre-installed, Brown concentrated on the compressor/condenser area. The front bearing and housing O-ring showed the “glow of death”, so the compressor was definitely DOA. Removal was the usual knuckle-skinning job on the little front driver, complicated slightly by the extra long mounting bolts that must be removed with the compressor.

Tearing down the compressor revealed telltale blackened oil and hardened sealant which was judged to be a chemical reaction between two incompatible chemicals. The buildup of sealant on the compressor shaft had allowed the system to leak out most of its refrigerant. The vanes were stuck into the rotor due to the gluing effect of the hardened sealant. That explained the lack of pressure despite lots of compressor RPM. Maybe adding a brew of chemicals might not have been such a great idea.

Vane seizure is common on these Matsushita units due to overheating. “They are built with very tight internal tolerances” commented Brown. Since the compressor is manufactured with a heat sensor, it must also be changed as it obviously didn’t do it’s job!

The compressor was cleaned out and tested by the SPI compressor team. The customer replaced the condenser and receiver dryer, and flushed out the system again. Then he mounted the overhauled compressor, added oil and brought it back for a recharge.

On startup, the compressor ticked loudly at idle. The tapping noise diminished when revved up and the air was cool, but nothing would relieve that annoying buzzing noise from this freshly overhauled compressor.

So we asked the installer “How much oil did you put into this compressor and where did you inject it?” Answer: By the Honda book, 3 oz into the suction port. WAIT! The Professor’s calls for 1.5oz. And, strangely enough, the oil belongs in the Discharge port on this Horrible Little Unit.

Professor Brown, with Centennial Apprentice students Dave Trotter and Sisay Tessima, immediately discovered that something was amiss.

The compressor noise was highly suggestive and the second teardown of the unit revealed the cause and results. The vanes were damaged on their tips, the housing end plate was gouged and the discharge reed valves were bent. Only one condition can cause this destruction – too much oil.

The synthetic ester oil was appropriate for this repair, but the quantity and point of injection was crucial. Checking with the installer, the correct amount of oil was added according to Honda’s manual …..but the point of injection wasn’t mentioned. This Matsushita has an internal pressure oiling system that puts the oil reservoir on the discharge side – where the pressure is- and that’s where the oil must be installed. By introducing the oil into the compressor through the suction port, enough hydraulic pressure was built up inside the compressor to cause damage. Brown explained the significance of the oil injection point: “The compressor is designed to compress gas, not liquid. When the oil reached the point of highest compression inside the unit, the liquid had nowhere to go. So it acted as if it was an abrasive solid, scraping out the housing, peeling away the tips of the vanes and bending the discharge valves out of the way.”

The SPI manual, authored by Professor Brown, specifies 1.5oz for this unit to avoid this type of irritating damage. Since the oil is also the coolant for the compressor, Brown recommends checking the temperature of the compressor body after 10 minutes of running – it should be between 40 and 60C. Too hot and it needs more oil, too cool, and it needs some removed. Do this an ounce at a time.

Brown uses a 60cc medical syringe to meter the oil into each component and is scrupulous about cleanliness and the need to keep lines and components sealed until just before assembly to minimize the amount of moisture introduced into the system. Brown recommends saving the plastic plugs that come with new components and use them to plug lines and parts when they are disconnected. He also notes that flushing is not an option, but a necessity where the compressor has failed catastrophically. Mufflers and condensers that trap debris won’t clear with flushing so must be replaced. Adding an in-line filter is cheap insurance to prevent orifice tubes or TXV’s from plugging.

Once assembled, being sure the system is pure and dry before charging is important. Brown recommends filling the system with nitrogen to check your work for leaks and by letting it out, the dry nitrogen will adsorb and carry out moisture. Then evacuation with a good vacuum pump must be done. The pump must be capable of pulling a 29.8″ vacuum and only a well maintained pump can do so. A vacuum less than that will not remove moisture. Since the oil in the pump self-contaminates as it sucks moisture out of the system, it must be changed every 10 days in a busy shop to maintain efficiency.

Forget that, and the pump will actually rust away inside.

With the compressor repaired and the correct amount of oil in the system -installed in the high side, the Civic ran refrigerator cool.

And that troublesome Matsushita vane compressor? It received 1.5oz, injected into its discharge port, and runs smoothly and quietly. In automotive air conditioning, excessive oil is definitely too much of a good thing.

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