AC gauge pressures - r134a

[jrobie79]

Just finished up my r134a conversion last night, went the whole 9 yards:

- custom barrier hoses to replace the rubber
- new compressor
- new condenser
- new drier
- new expansion valve
- o-rings with Nylog throughout
- M44 aux fan (puller mounted on radiator) - deleted stock aux fan &
mechanical fan

I charged it up last night with my gauges, and its definitely running colder, I didn't have a thermometer so I can't be 100% certain, but the vent temps at idle didn't feel any colder than probably 60°.

I took a snapshot of the gauge pressure readings early this morning, conditions were 86°, humidity 63%.

Does this look right? Seems my low pressure reading might be a little high? Not sure how it works in conjunction with the high pressure reading and if I overfilled or not.

[jeffnhiscars]

What I've learned...and really should do a write up..is that the quality of the vacuum really outweighs the charge and to some degree, the state of your hardware.

In short, without a micron gauge it's all guess work when the target is 500 microns. Our manifold gauge goes to minus 30 over about an inch of dial which means each inch is equivalent to about a mm. Given that there are 25000 microns to an inch you are simply flying blind in knowing when a proper vacuum is done.

I messed around with my cabrio for a couple of years..topped up a couple of times each season until I replaced the 2 hoses above the glovebox with custom upgrades....still had marginal performance. Keep in mind there are no OE parts left...pf condenser, Seltec compressor etc.

I finally got a micron gauge and got some guidance from the mfg how to read it. I'm paraphrasing so please don't quote me but what happens is that, depending on how much humidity is in the system it can take way more than an hour to get a tight system down to where it should be. When you isolate the system and THEN turn off the pump, that's when you learn. A good system will rise a few 100 microns over a few minutes due to the absence of the pump...BUT...if it goes to say 11-1200 you still have humidity flashing off. If it continues to rise you have a leak so fix it.

However, if you had enough humidity that some may have condensed, it will settle in your compressor and hide with the oil and has to be coaxed out. In my case I left the pump running for 3 days and every time I turned it off the check, it would rise too much. I was getting down to 1000...then to 800...then finally down to 500.

I also used a core removal tool since sucking through the Schraders gives you 10% of a full flow and given my hose fittings I pulled through the drier (doesn't matter). I know I let a bit of air back in while farting around with fittings, but got 2 cans in (24oz) and am glad to say it's comfy in the Florida summer without my hard top.

Bottom line is "tight and dry" and with out the proper gauge you are totally blind....at least that's how I see it

[TobyB]

From the chart I have, both pressures are on the high end,
but the discharge temp IS supposed to be around 60.

hth

t