AC help please! So hot. I need proper pressures.

[mistertonylee]

Hi all. So, a couple weeks ago I blew an ac hose (from compressor to front of car in front of radiator). For some reason, there was no heat shield and it was 1/2 inch from the exhaust manifold. I replaced the hose, bought a manifold gauge set, and refilled the system with PAG oil and r134a (system was professionally converted a few years ago).

The problem is I don't know what the proper pressure is. I've tried anywhere from 30-45 on the low side (300-250 on high side). It blows kinda cold, but not what I need it to. I mean it's 90 degrees today with no end in sight. :firehop:

Does someone who has converted to r134a and who has cold ac and a manifold gauge tell me what their pressures are and the ambient temperature. I can't find any kind of specific standard for e30s. If early/late e30s have different systems, I have a 1984 325e.

Thanks

Tony

[jlevie]

An E30 converted to R134a won't ever have really cold air. The evaporator and condensor are too small for that refrigerant. I've had lots better success with Freeze-12 and even better success with R12 (though it is pricey and hard to get).

[mistertonylee]

Yeah. I know there are better options, but I had the 134a lying around, and it was cooling pretty well before (I don't know the prior pressures). I might try the Freeze-12 conversion if I can't get it back to where it was before the hose burst, but I'd like to try the proper charge of this first. BTW, any word on the compatibility of 134a with the Freeze-12? I'm assuming that a vac on the system would be enough?

Thanks

[Ryann]

An E30 converted to R134a won't ever have really cold air. The evaporator and condensor are too small for that refrigerant. I've had lots better success with Freeze-12 and even better success with R12 (though it is pricey and hard to get).

False. The OP's problem is that he didn't pump the system down before recharging. Your head pressure is through the roof because your system is contaminated by atmospheric air. As a rule your gauge needles should point in the same general direction, as an example 10 o'clock/10 o'clock.

[mistertonylee]

OK. I tried to vac the system when I charged it before, but I screwed it up (stupid clockwise to open valves). Now that I know how, I can do that right this time. Anyone have a rough idea of how much refrigerant the car holds or what the pressure should be at, say 80 or 90 degrees?

[PorkandBeans]

Bentley says R-12 capacity is .975 grams (2.1 lbs.)

I just added some 135a to my converted system due to a small leak and just used the generic chart on the bottle. I was at like 22 psi low side (75 F ambient) and topped it off per the chart. I bought a 18 oz. can and it still feels half full.

ambient 75 F - 35-45 psi
ambient 80 F - 40-50 psi
ambient 85 F - 45-55 psi
ambient 90 F - 45-55 psi

[nrubenstein]

An E30 converted to R134a won't ever have really cold air. The evaporator and condensor are too small for that refrigerant. I've had lots better success with Freeze-12 and even better success with R12 (though it is pricey and hard to get).

Well... I had to turn on the recirc function to get good performance (especially as it was really humid that day). On the other hand, I still think R134a performed reasonably. The following pictures were taken at fan speed 4. The TWC App said 93 degrees, so I believe the OBC temp sensor was reading accurately, after all it was sunny and pavement soaks up heat.

Highway:


Idling for 5 minutes:


It's certainly true that R12 is better, but the fact remains that R134a can provide perfectly adequate service.

[Ryann]

At those temps. your discharge pressure ought to be around 175 to 225 psig depending on engine bay temp., humidity, aux. fan speed...

Pump it down properly, charge using the sight glass with the system on full blast/windows up when it's hot out, and consider the gauge needle rule. You'll be golden.

[nrubenstein]

At those temps. your discharge pressure ought to be around 175 to 225 psig depending on engine bay temp., humidity, aux. fan speed...

Pump it down properly, charge using the sight glass with the system on full blast/windows up when it's hot out, and consider the gauge needle rule. You'll be golden.

Or, as stated in the other thread, fill by weight. :) It works for me.

[mistertonylee]

Wow. Thanks for all the responses. I'm putting a vac on the system this morning and charging. For some reason, I don't have a sight glass on the receiver drier, but without outside air in there this time, I should be able to make minor adjustments to get it right.

[LJ851]

Since you dont have a sight glass this might help. A couple pages down it lists R134 volume by weight.

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

[mistertonylee]

^Extremely helpful document. It turns out I still need about 2 oz. of 134a to be completely full (I used the 0.9 x R12 amount -1/4 oz. forumla and came up with 29.99 oz.). This says about 32 oz. I ended up using 28 oz. 134a + 2 oz. PAG oil.

I actually evacuated the full system this time instead of just the manifold gauges (do'h). It performs much better and should be fully satisfactory once I add a few more ounces of refrigerant.

I'll post my final pressure readings with ambient temperatures once I add that last bit.

[Ryann]

^Cool!

[mistertonylee]

OK. So I evacuated the system and added 2 oz. PAG oil and 31-32 oz. R134a. That corresponds to 35 PSIG on the low side and 350 PSIG on the high side at 1500 rpm, 87 degrees ambient temperature, about 40% relative humidity.

It cools very well, and the low side hose is sweating a good deal, so I am assuming that the recharge is successful. I'll try to pick up a kitchen thermometer to measure the temp of the air at the vents soon.

I did discover that the recirculate feature on my car isn't working properly. I had to remove the cover for the blower motor housing and manually close the flaps to get it totally into recirculate mode. Anyone have any idea how to maybe lubricate the linkage or something to get the flaps to work properly?

[mistertonylee]

Also thought to ask: Is the compressor supposed to cycle on and off? Every american car I've had does so, while every european one doesn't. Any ideas?