Originally Posted By: Doog
UPDATE: Ok so I went to HF and bought the manifold gauges. Put them on the car and both showed a low refrigerant charge. Added in about 1/2 ounce of IR dye and maybe 8 ounces of refrigerant ( the normal charge is 16 oz.) to get the low and hi side gauges to come up to spec according to my Honda chart. Took it for a 5 mile ride and with the air on low speed fan (recirc off) and set to the lowest temp my thermometer is showing 42F at the port. (Not bad for a 2009 with 110k IMO since my new Avalon runs at 40f). So, now I'll let her drive it for several weeks and check with a black light for leaks.
A quick primer on evaporators :
Liquid enters the bottom of the evaporator, boils as it absorbs heat and leaves the top of the evaporator as *mostly* vapor. If you have insufficient refrigerant you end up with entirely superheated vapor leaving the evaporator. The problem there is the system relies on the "mostly vapor" part to have enough liquid in there to transport oil. So if you have an insufficient charge you end up with an increasing pool of oil sitting in the evaporator. This impacts cooling as it impairs evaporator efficiency, but worse is it slowly starves the compressor of lubricant. The compressor wear rates increase, which pumps out fine metal grunge into the system. This lodges in the condenser, pipework and expansion device and is why they generally need replacing when you do the compressor (it generally looks like a fine aluminium coloured valve grinding paste). Keep your refrigerant levels up and these problems occur much less frequently. Most compressors don't die, they are killed due to lack of lubrication.
So, the point of that was to say be careful about putting in refrigerant to get the "gauges to come up to spec" as you may well not have enough in there to properly transport oil.
This is also why it really doesn't hurt to have a system "re-gassed" (ie weigh out, weigh in) every couple of years. It'll make things last a lot longer in the long run. All systems leak. Newer are better than older, but they still leak. Now 20% loss in charge on a big system may not impact the performance enough for you to notice, but it certainly will impact oil return and system overall longevity.