E30 + R134 = not impressed

[LJ851]

Just bought some manifold gauges, stay tuned.

[nrubenstein]

Just bought some manifold gauges, stay tuned.

Hope you bought a scale and a tank so that you can properly charge it? Everything I've seen says that R134a basically just can't be accurately filled based on pressures or the sight glass. (And my experience with it bore that out, too - performance was complete crap until I sucked it up and filled by weight.)

[TrentW]

The shop that does my a/c still has a secret stash of R12, so I'm thinking I'll just stay with that for now and replace my leaking Denso compressor and rec/dryer, then do the 134a conversion whenever the R12 supply runs out. I'm looking at rebuilt compressors and BMA has a Nippondenso unit that appears to be the same as mine. I wanted to talk to Patrick, but he was busy on another call, but Sergio called me back after checking with someone and said that it can be used with R12. Can anyone verify that that's the compressor I should get? I know the compressor oil is different for 134a and curious if this guy knows what he's talking about.

[LJ851]

OK. I hooked the gauges up with the Knobs turned all the way in and the the pressures are:
With engine idling , a/c on max ,52 psi and 215 psi.
With engine at 1500- 2000, a/c on max ,35 psi and 225 psi
Am i doing it right and how do those #s sound? Vent temps are 80 degrees at idle.

[CorvallisBMW]

According to the p/t chart for r134a, you're sitting at 56F suction (low side) and 135F discharge (high side) when at idle. So I'm not surprised the vents are blowing warm, but I would expect them closer to 60F than 80F.

However 35psi = 40F, meaning you should definitely see cool air. General rule of thumb is that air leaving the evaporator will be about 10F above the low-side temp. So again, I'd expect to see temps lower than what you're getting.

http://www.csgnetwork.com/r134apresstempconv.html

[Hey_You]

Also remember, that if you have more than 2% air in your system than it can cause your a/c to blow warm too. Only way to tell is with an Identifying machine. R12 is the way to go if you have a leak as it is larger molecule so it leaks slower, but at over twice the cost of R134a, is it worth it to you?

[Ryann]

OK. I hooked the gauges up with the Knobs turned all the way in and the the pressures are:
With engine idling , a/c on max ,52 psi and 215 psi.
With engine at 1500- 2000, a/c on max ,35 psi and 225 psi
Am i doing it right and how do those #s sound? Vent temps are 80 degrees at idle.

Your suction pressure is too low and your discharge pressure is too high.

You probably have some moisture in the system that is plugging up your expansion valve, which is starving your evaporator giving you your shitty warm vent air. You could also have a faulty expansion valve or sensing bulb. The fact that your discharge pressure is high (assuming it wasn't 100+ degrees outside when you got your reading) would indicate that your system is also contaminated with atmospheric air.

To fix it right (assuming the TXV is not faulty) you need to do an r11 flush and replace your drier. Then you need to charge the system with dry nitrogen for a couple hours to soak up any remaining moisture. Then you need to pump the system down to a 500 micron vacuum for 1/2 hr.+ before refilling with 134a.

I disagree with several other posts concerning a certain percentage of charge by weight. The best possible way to charge a clean and converted system is to clear the sight glass under the conditions in which the system will be expected to run.

[nrubenstein]

IIRC, the E30 takes 27.5 ounces of R134a. You can be a couple ounces over that. I fill to 29.5 to account for hose losses.

That said, Duracool/ES-12a/HC-12a works a lot better. My vent temps have been pegged at 32 degrees since I switched (no matter what fan speed - which suggests headroom). It hasn't been hot here yet, but I'm really looking forward to seeing how the system does then. Ironically, I found that you have to fill with HC-12a by pressure. I tried by weight and was WAY high on pressure.

I take it back. Duracool/ES-12a really seems to struggle when things get hot. Moreover, pressures start going crazy and I was getting occasional compressor lockup.

I've switched back to R134a.

Filling by weight and using recirc, the car is blowing 36 on the highway with the fan set to 4. After idling in the driveway for five minutes, I'm showing 42. I can not emphasize strongly enough the value of filling correctly by WEIGHT. Ambient temp is 96-97 according to the car, 93 according to the weather channel app.

The reason why you fill by weight is because you can be pretty much dead consistent every time. It may be that a truly skilled individual can fill by the sight glass (although the literature that I've seen suggests that this is crap), however, I am not a truly skilled HVAC tech and I suspect that that goes for the rest of us. Filling by weight is easy and precise and consistent and it WORKS.

Also, use recirc when it gets hot. That'll drop your vent temps by a LOT. I suspect that the evaporator is just too small to effectively cool really hot air.

[Ryann]

I can not emphasize strongly enough the value of filling correctly by WEIGHT.

I 100% agree with this when charging a system with the original gas. Also, the jug is ALWAYS on the scale when I'm charging a system.

However when charging with drop-ins or after a conversion, weight percentages are only a guideline. Using the sight glass you will often times be able to stop short of that guideline depending upon the conditions under which you expect your system to run.

[nrubenstein]

I 100% agree with this when charging a system with the original gas. Also, the jug is ALWAYS on the scale when I'm charging a system.

However when charging with drop-ins or after a conversion, weight percentages are only a guideline. Using the sight glass you will often times be able to stop short of that guideline depending upon the conditions under which you expect your system to run.

*shrug* Maybe. The thing is, though, that the guideline works pretty well and is eminently repeatable. Particularly given R134a's low tolerance for mis-filling, you really shouldn't be too far off of that anyway. Again, maybe a competent HVAC tech can do a consistent fill with gauges and the sight glass. I will state flat out that I can not and that when I go by pressures or what I see, I usually end up grossly undercharged or overcharged.

What I'd like to pull up is BMW's recommended R134a fill. I'm quite certain that it's out there given that they created their own retrofit package.

[Schnitzer318is]

^You are much more experienced than I... but the guys at the shop always fill by weight original or after a conversion. From what I have gathered just from personal experience the sight glass is not a reliable way to fill unless you are starting with a completely fresh or fairly young system using the original gas.

Of course ymmv as I am only reporting personal experiences on my e30's.

[Huff]

*shrug* Maybe. The thing is, though, that the guideline works pretty well and is eminently repeatable. Particularly given R134a's low tolerance for mis-filling, you really shouldn't be too far off of that anyway. Again, maybe a competent HVAC tech can do a consistent fill with gauges and the sight glass. I will state flat out that I can not and that when I go by pressures or what I see, I usually end up grossly undercharged or overcharged.

What I'd like to pull up is BMW's recommended R134a fill. I'm quite certain that it's out there given that they created their own retrofit package.

Ditto.. Any idea's on where to get that info? I have a factory converted R134 e30, but the stickers are missing.. So, I don't know what BMW recommended with their conversion. But I would love to.

[LJ851]

I saw that somewhere here...

...Here it is, BMWs R12 to R134 retrofit guide. There are complete instructions + the charge weight of R134 .

https://docs.google.com/fileview?id=F.5b73ad14-d731-45ec-aa6f-4784b0e7d67a&hl=en&authkey=CNO6w-8O

[nrubenstein]

Interesting. I guess I've been underfilling slightly. That calls for 31.68 ounces, plus or minus .8 ounces. I've been filling to 30 on the scale. Guess I'll add a couple ounces at some point.

[LJ851]

Ryann has encouraged me to whip this A/C system myself, so im going to go for it. A/C is the only vehicular system i am not intimately familiar with (besides autotragics which i refuse to give the time of day) and im due for a challenge so here we go.