[s-cars] AC recharge

[Kunz, Bob]

Green aliens from Planet Osmosis made Theodore Chen say...

> the air conditioning system in my '92 works, but not very well.  
>
> a shop said they'd recharge it with R-12 for $120, or convert to R134a for $140.

Ah, summer arrives and the inevitable A/C issues crop up. You should keep the system R12 if possible because of all the issues already pointed out.

The low pressure port is the low pressure switch (in the plenum on the passenger side). You remove the switch and bridge the connector (keeps the system from thinking pressure is too low), the system remains closed because there is a Schrader valve in there. If you've got manifold gauges use them of course. Low side pressure depends on ambient. A couple of data points are (degrees F, PSI) (77,29.5), (86,29), (95, 30). This is with the engine at 2K RPM, max cool, high fan. Some compressors (my '86 does) have a low pressure port on them in which case the pressures are about 3 PSI lower taken at that port. If you need to play with the high side, you also remove the switch and leave the cable connected (makes the system believe you are not over pressuring the system on the high side).

Remember the rule about recharging R12 systems (EPA tech hat on now)... you CAN top up systems that are leaking but if you need to open them you MUST recover the refrigerant. That's what makes complete service of R12 systems pricey. $140 means the shop you queried is not following rules. And although R134a is the same stuff in duster cans, if you are dealing with it in a refrigeration system you must recover the R134a. Go figure!

--bob
'86 5Ks Avant
'99 A6 Avant
'02 TTQR
'07 Q7 4.2P