What are your HVAC pressures and dash temps
05-28-2019, 02:25 PM
#61
Chronic Tool Dropper
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Charging without evacuating will --always-- give you a foamy flow to the expansion valve. Air in the system is one of the necessary ingredients for corrosion to start. Air in the system will easily steal 15º of evaporator temperature, if only for the fact that the boiling pint for the refrigerant goes up as pressure increases. Air also hogs condenser capacity by gathering in the top tubes. Air doesn't carry lubricating oil to the compressor. The list is longer than my fingers want to type this morning. Regardless, any single item on the effects list is reason to evacuate, make sure you have the correct amount of oil in the system, and recharge correctly.
05-28-2019, 02:38 PM
#62
Three Wheelin'
Thread Starter
would you agree that I have the correct fill, and to refill to the same amount?
05-28-2019, 03:26 PM
#63
Chronic Tool Dropper
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All it takes is a fraction of a second open to induce air, unless there is sufficient pressure in the system to push refrigerant out. If you open the system and let it go to atmospheric pressure, you'll have air in there.
If that air has moisture in it (and it does...) you'll want to vacuum the system long enough to boil that moisture out through the vacuum pump. The receiver/drier is tasked with scavenging moisture from the refrigerant and oil in the system. Inside is a bag of dessicant material which does the actual absorbing and holding. That bag and the dessicant granules inside become saturated with refrigerant oil the first time you run the system, making it virtually impossible to use vacuum to boil out the accumulated moisture. Hence the generic recommendation that you need to replace the drier every time the system is opened. The oil is hygroscopic too, so any extended open time demands new oil along with the drier.
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There are (or used to be) AC system specific manuals from Haynes, for instance. They don't speak to 928-specific systems like the system controls, but do offer some seriously in-depth guidance on the refrigeration side. There are undoubtedly similar online resources.
Way back when (early 1970's), I took a course in auto AC at the local junior college. Eight weeks of two hours a week, plus "lab" time in the auto shop where students could bring their troubles to class and have a hands-on clinic. The classroom time was spent on theory, plus the practical side of actually servicing systems in cars. The manual from that class was a couple inches thick of serious textbook, plus a working notebook. Worthwhile looking into if you really want to get a good working knowledge of the refrigeration side.
If that air has moisture in it (and it does...) you'll want to vacuum the system long enough to boil that moisture out through the vacuum pump. The receiver/drier is tasked with scavenging moisture from the refrigerant and oil in the system. Inside is a bag of dessicant material which does the actual absorbing and holding. That bag and the dessicant granules inside become saturated with refrigerant oil the first time you run the system, making it virtually impossible to use vacuum to boil out the accumulated moisture. Hence the generic recommendation that you need to replace the drier every time the system is opened. The oil is hygroscopic too, so any extended open time demands new oil along with the drier.
----
There are (or used to be) AC system specific manuals from Haynes, for instance. They don't speak to 928-specific systems like the system controls, but do offer some seriously in-depth guidance on the refrigeration side. There are undoubtedly similar online resources.
Way back when (early 1970's), I took a course in auto AC at the local junior college. Eight weeks of two hours a week, plus "lab" time in the auto shop where students could bring their troubles to class and have a hands-on clinic. The classroom time was spent on theory, plus the practical side of actually servicing systems in cars. The manual from that class was a couple inches thick of serious textbook, plus a working notebook. Worthwhile looking into if you really want to get a good working knowledge of the refrigeration side.