Originally Posted By: Brad_C
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.
This is all great text book stuff, but the reality proves otherwise. "re-gassing" the system every few years is probably the worst idea ever for the longevity of the AC system, unless you have a shop that can be 100% trusted. Even then, opening up the system so often is simply an invitation for something to go wrong. Every single hook up of the gauges invites moisture, even if the tech purges the lines, which I highly doubt they do since 1) releasing refrigerant is illegal and 2) they would not want to waste the product.
Leaving the system alone, operating it periodically even during winter by using the defrost setting, occasionally cleaning the condenser and if equipped, changing the cabin air filter, is simply the best one can do for the AC system in the long term. There is nothing wrong with topping the refrigerant off if the performance starts to suffer.
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.
This is all great text book stuff, but the reality proves otherwise. "re-gassing" the system every few years is probably the worst idea ever for the longevity of the AC system, unless you have a shop that can be 100% trusted. Even then, opening up the system so often is simply an invitation for something to go wrong. Every single hook up of the gauges invites moisture, even if the tech purges the lines, which I highly doubt they do since 1) releasing refrigerant is illegal and 2) they would not want to waste the product.
Leaving the system alone, operating it periodically even during winter by using the defrost setting, occasionally cleaning the condenser and if equipped, changing the cabin air filter, is simply the best one can do for the AC system in the long term. There is nothing wrong with topping the refrigerant off if the performance starts to suffer.
