Add R-134a??

[JHZR2]

Car is 91 318i, OE had R-12 but did a complete (new compressor, full flush, etc) retrofit to 134a in 2004.

Blowing around 60 in 80-90 degree, 50-60%RH weather.

Today, 82F outside.

Only at idle, no helper to hold it up at higher rpm, but if I do it, more like 15-20psi low side. Box fan plus engine and aux fan all working.

 

[Roadkingnc]

The only way to tell if it has the proper charge is to have an evac and recharge done on it. What does the high side do if you raise the rpm?

 

[JHZR2]

High side stays roughly the same or drops a bit (mechanical fan so more airflow). Low side will drop to 15-20.

The charge has been in there for nearly 10 years now, and has needed no appreciable top-ups so there's no real chance of air in there.

A bad expansion/orifice, perhaps. Not sure what the car has...

 

[demarpaint]

Originally Posted By: Roadkingnc
The only way to tell if it has the proper charge is to have an evac and recharge done on it. What does the high side do if you raise the rpm?


+1 otherwise all you're doing is taking a good guess and will never really know if the AC is properly charged or not.

 

[JHZR2]

Originally Posted By: demarpaint
Originally Posted By: Roadkingnc
The only way to tell if it has the proper charge is to have an evac and recharge done on it. What does the high side do if you raise the rpm?


+1 otherwise all you're doing is taking a good guess and will never really know if the AC is properly charged or not.


Well it's a retrofit, so it's all rules of thumb anyway...

 

[Roadkingnc]

It is low then but how low is anyone's guess. You can add some but the stuff you buy in the small cans usually has some sort of stop leak in it. It should have dye in it, a black light will make the leak stand out.

 

[JHZR2]

A leak??!? The system has held tight for nearly 10 years.

I have a 30# container of 134 and real gauges. Just looking for rules of thumb for topping up.

The standard interdynamics chart says that at 80F, low should be 40-50, and high should be 175-210.

No way my high side would be that low with the low side >40.

 

[JHZR2]

FWIW a BMW document I found says that for roughly 45% humidity and 80F, pressures should be 36 and 164 for r-134a in their cars.

However that likely assumes that the vehicle doesn't have a tube-fin R-12 condenser, which my car does. So the delta on pressure needs to be determined as it should be higher.

The car specs 900g for a 134a retrofit.

 

[yonyon]

Well, if you just want some general "rules of thumb" then here's one.

With everything on high and whatnot and the engine at a stable speed around what would be expected cruising on the highway the low side should not drop below 28 psi for more than 3 seconds.

 

[JHZR2]

Good stuff... I can't get there without the pressure probably going over 300 on the high side.

I added a little just to see what would happen...

Low side stayed roughly the same, while high side started to increase, so I stopped. Low side increased a bit, so the min pressure under raised rpms is higher, and my vent is more like 55F... But high side was going up past 210psi, and I didn't want to go there.

The BMW values make no sense with this. But again, I think they assume parallel flow and thus the values cannot be trusted.

Adding some dropped temps, no way taking pressures to 160psi high side would cool, IMO. Seems this indicates that I'm NOT overcharged, but can't take high side high enough to get low side right.

Thoughts??

 

[yonyon]

It's been a while since I did a retrofit and back then I would always put the megafan in front of the car before adjusting the charge. With just the vehicle fan in place I looked to 260 as an upper limit on the high side with ambient in the upper 80s to low 90s.

 

[JHZR2]

Actually, I saw some drop so I kept adding. Wanted to let low side get to 36 at least, based upon the BMW documents I'd seen.

Added some more, pressures rose. Didn't want to go past 275. Figured of I overcharged, I'd just pay a shop to evac and dump 900g in.

Took it to 35ish and a hair over 275 at idle (drops a bit when spinning). On the road, like 2000 rpm and 30mph, I'm seeing 44, and up to 48 when stopped at lights. Going up in pressure helped here, for whatever reason.

I'm not going to try for any better given the pressures and the fact that I have an r-12 condenser. I'm sure if I put a parallel condenser in, I could get it to 40F.

 

[yonyon]

This sounds pretty good but it's just warm out right now. Don't be too surprised if you see lower performance on a hot afternoon.

My magic 8-ball says you're probably a couple ounces overcharged but then retrofits can be a bit unpredictable.

 

[another Todd]

Originally Posted By: yonyon
This sounds pretty good but it's just warm out right now. Don't be too surprised if you see lower performance on a hot afternoon.

My magic 8-ball says you're probably a couple ounces overcharged but then retrofits can be a bit unpredictable.


I was thinking the same thing. A Little overcharged with low side in the 45 range.

 

[JHZR2]

No my low side is in the 35 range. The official BMW documents say that for my conditions, I should see 36 psi low side.

My problem is that my high side is too high. But it's cooler than it was when I started the day.

In the 99 degree weather a few weeks ago, it couldn't go below 62F, and that's where it was blowing when I started the day today. Yeah, it's cool out, but the system was not working right previously.

I'm actually surprised that the system takes 900g of 134a, given how much colder and less refrigerant the newer systems take.

 

[JHZR2]

Granted its only 63F and 91%, but I'm down at 40F.

 

[meep]

too high on the high side might suggest problems with the orifice. IDK if your car runs a variable one or not. some do.

also, the internal sealants in those r-134 kits can sometimes build up and restrict the orifice, in many cases clogging it completely. hopefully that is not the case here.

 

[JHZR2]

I've never used a "kit" or any sealant of any sort.

The expansion valve was replaced when retrofit. It uses a sealed sample of 134a in there to operate it (however it operates).

After a few hundred miles, with daylight, 80F and a bit more humidity, im at 56F or so. Cooler than the consistent 62F I had before, more comfortable for sure, but not as good as last night.

 

[Vikas]

If this were my car, I would add little bit of (only) refrigerant (very slowly) (1/3 can at a time) and STOP as soon as it becomes colder.

 

[JHZR2]

I don't add by can, I have 30#.

I did just that, but have to be reasonable about pressures.

To make things more odd, AC was cool this AM, then refused to go below 60 when the outside got up to 90F. Now it's down to 84F, and it's blowing 44F again and is very cold.

Wonder if evap is freezing up...