Date: Sat, 02 Jul 2005 05:20:35 GMT From: Malcolm William Mason <mwm1(spam)nospamedu> Subject: Re: Re: Re: A/c compressor 1999 9-3
On Fri, 01 Jul 2005 06:23:32 GMT, "James Sweet" <jamessweetnospamail.com> wrote: perhaps I exaggerated when I said pump down for hours but as noted, the vacuum is never too good and 30"Hg. is adequate. If you can attain more, so much the better. >Is the receiver and dryer not a combined unit on this system? Admittedly >I've only worked on Volvo automotive A/C systems and domestic central A/C, >the former having a combined reciever/dryer and the latter normally lacking >a reciever entirely. If the receiver dryer is one combined unit, It does no harm to leave it in place and simply add a generic filter/dryer. Please note filter/dryer! The original system may only have had a dryer and (I believe) some OEM stuff does not have an original dryer most do not have a filter. It is not required to change the receiver whether it is combined with the dryer or not. It is all right to leave the old dryer in place but cut it out if it is easily done. Used it has saturated silica gel, new the gel is anhydrous. but an old dryer creates very little resistance to flow. nothing important,but there is a tiny value in removing it. After replacing the compressor, which is almost always the case, always add a filter. A new filter. The failing of failed compressor creates a lot of crud that you do not need fouling the replacement. I have seen sticklers who after a week or so will remove and reinstall another filter dryer pump down and recharge. This may be a "belt and suspenders" approach, but those who did it had plenty of automotive cooling experience. Email direct if I can add to this. Malcolm >As for the vacuum, it's true that you can never have too good of a vacuum, >however it's not usually necessary to pump it down for hours. An hour with a >decent vacuum pump should be sufficient, then shut the valve and monitor the >vacuum for a half hour or so, if the pressure increases on it's own then you >either have some moisture still in the system and need to pump it down >further, or more likely a leak which needs to be fixed. The vacuum doesn't >have to be super high, but it should be darn close to 30 in/Hg. A rotary >compressor such as used in window A/C systems is normally more than >sufficient but the lower you can get the pressure the more efficient the A/C >will be. > >The dryer *always* needs to be replaced whenever the system is opened since >it will quickly saturate with moisture from the air, and the orifice tube if >used should at least be inspected but after a compressor failure it should >certainly be replaced. If this system has a TXV* then that will normally need >replacement too but most newer systems use a simple orifice. > It does not hurt to replace an orifice or a capillary metering tube but if the type of connections permit it , cleaning either up is acceptable. *TXV is thermal expansion valve Malcolm
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