Bret 944

Cool. Thanks, I may pick one up then. Not too expensive, probably worth it to just go ahead and put one in.

jim302

What the heck is OK range? I own three sets of gauges and none of them indicate OK or not OK

What happened in your sight glass?

The best way to "backyard" charge your system is to watch your sight glass. When the bubbles stop add only a little more. The drier functions as an accumulator and the high side should hold close to the same pressure until over full. If there is any increase in pressure after the bubbles stop, the system is over charged.

The gauges are a great tool for trouble shooting using real pressures.
An example would be 10 psi on the low side and 320 psi on the high side means a restriction in the system. (Probably drier or expansion valve)

Bret 944

I actually haven't checked the high side pressure, low side only. Hopefully it's not raining tomorrow afternoon and I can go out there and mess with it a little more.

Zero10

Tony, those cycle times sound pretty good. When mine is properly charged, and blowing cold, that's pretty much what they are. It does cycle a lot more often on cooler days, but I like my car cold, so sometimes I'm running it when it's only 15*C outside, or sometimes the sun is hot enough, even though the outside air isn't all that warm. Or it's raining, or whatever, so it gets it's fair share of usage in cooler weather. When that's the case, at idle, it goes about 10 seconds on, 10 seconds off, almost exactly. When cruising, it's more like 6-7 seconds on, 10 seconds off. The 'off' time pretty much never changes, only the 'on' time, which on a warm day can go 20-30 seconds some times.

If charging with r134A or r12, you want no bubbles in the sight glass. I found that if I fully charge a system, the low side pressure stays the same for the last part of charging it, and only the bubbles get smaller, then go away completely. What I do, is only open the valve a little bit when I know I'm close, and once the bubbles are gone, take my time shutting the valve off. Should give it roughly that last little bit. What I have also found, is that as the system loses a charge, the low side pressure will sometimes stay within the 'ok' range, and yet I can get pretty large bubbles in the sight glass.

I've seen a few gauge sets that have colored regions with labels like 'low' 'ok' 'warning' 'danger', or things like that, usually on the more DIY oriented sets. Usually the 'ok' range is from 35-45psi on most of these sets.

At 80-85*F, I would advise you charge it to about 40psi on the low side but do make sure the high side is within spec. This can be challenging if you don't have a good set of gauges.

I've never changed an expansion valve on these cars, but when I look at the pictures, it looks like one end is soldered in?
It's under the blower cover, remove the big black cowl cover, the blower unit, and you'll pretty much be staring at it.

zainman

I don't understand why people convert to 134a when there are direct replacements for r12. I'm in the refridgeration buisiness and do this all the time, and it is a lot less exspensive because you don't have to change a thing.

Zero10

Yep, there are hydrocarbon refrigerants that are a direct replacement for R12, and if the replacement is not a hydrocarbon refrigerant, it most likely IS R134A, as discussed in another thread on this topic.

There is not a lot of work in a R134A conversion really. The only thing extra to do, is install the fittings. Ideally, if you're repairing an old leaky system, you would want to evacuate all of the old oil and everything even if you were refilling with a R12 replacement.

Hydrocarbon refrigerants just aren't safe, I had one car charged with it, and when it caught fire, it quite literally nearly blew the hood off. Because of that I will never use them again.

If there is a R12 substitute that I don't know about, feel free to enlighten me, as I am a fan of doing things in the simplest fashion.

F18Rep

Our temps here in St Louis are up in the 90's, and I must say to see a 20 year old Porsche slide by with the windows up - is an impressive sight. The wheels are cool, the paint work, great; but I look for the windows. If they are up THAT is cool.

Bruce ;]

Bill.e1

I think these cars have a high pressure cutout set at around 250psi on the high side. If you overcharge 134a, you will be hitting 250 quite often and the pump will cut out. If you don't see any bubbles in the site glass, you are probably overcharged with 134a. On mine, I charge to the point where most of the bubbles were gone and the low pressure cutout never tripped. It will still hit the hiqh pressure limit on hot freeway runs but it stays cool.

The expansion valve has a variable venturi- it senses the low side pressure and adjusts the pressure drop. One "optimized" for 134a might help but as long as you can get a good pressure drop, you are probably OK.

Make sense?
Bill
86NA

Zero10

No high pressure cutout. Makes it a bit more dangerous, no? Unless it's combined in the low pressure switch?

There is another 'high pressure switch' near the receiver/dryer, but if this high pressure switch sees excessively high pressure, it will turn on/up the rad fans. I see one or two bubbles every 10 or 15 seconds on a properly charged R134A system. You are correct, no bubbles is overcharged.

I don't know if the expansion valve is different on a R134A system, good point to ponder. I plan to change mine, since I think some 'stop leak' was used in the past, and the system was opened, so it's acting up.