A/C questions

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I now have some R12 and want to test the AC. It hasn't worked for 10 years.

I understand from previous posts I should first evacuate the system with a vacuum pump and then determine if there are any leaks. Is there anything else I should do first before charging the system?

Also, I never worked on a R12 system. I have a 72 0cs with the original compressor. I don't even know which is the low (to charge the system) or high valve. Is the suction/low valve the one close to the fender and the high valve closer to the engine?

Would appreciate any suggestions.

Thanks
 
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follow the hose that goes from the firewall directly to the compressor, this is the low side. The line from the dryer to the firewall is the high side so you can then follow that back to the compressor to confirm that fitting.

Hook the vacuum pump up to the low side, run it for 30 minutes, turn it off and see if the pressure rises back up over the next couple hours or even overnight. This will tell you if it is leaking or not before you go wasting freon. Turn the valves closed to isolate the system from the vacuum pump hose.

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Andre,
Those 40+ year old AC hoses look pretty tired. You may want to cover them with soapy water. Then if there are leaks you may see bubbles from the source.
Stan
 
Thanks Steve. I'm glad I asked. I would have thought the low side on the compressor would be closer to the fender and not close to the engine. It would have been slightly easier to to reach.

But what am I saying? This is BMW, "why make it easy if complicated works just as well".

When refilling do I have to do the same as in 134, that is turn the air on to the max while refilling?
 
A/c Hoses

You're right Stan. They are after all 42 years old.

Question, those hoses are very hard to the touch. Is this right or should they be supple/soft?
 
If your system is empty the compressor will keep shutting off and you won't be able to fill it unless you jump the wires, don't know which ones though.
 
original

red cloth covered hose has a braided metal jacket beneath. Yes, they are hard.

I suggest you make sure the fan works first. You can jump it. Or just find the ground wire that goes back to the round relay can screwed to the firewall down by the compressor. Make sure that can is tight as it grounds both the compressor and fan to the body.

A simple quick release of the schrader valve by the dryer will tell you if you have any pressure left in the system. If so, no need to evacuate. Could be just low charge.

Grab the compressor or pry on it to see if the mounting is as it should be. The bracket is two piece with old metalastic bushes to isolate the vibration. If it's loose that has to be fixed.

You need a long hose or guage set. As Steve said, the low side fill is on the compressor, closest to the block. It gets hot fast. Really hot.( Headers on mine)

Yes, fan on high, windows open, etc. I use a thermometer in the vent to read discharge. Try for 45 degrees. It will drop to 60 pretty fast, then take longer to get down to the correct discharge temp. It is a bit variable due to ambient and humidity. Mine for reference can blow to 42.

The repair manual has the info on charge, wiring, etc. Just look for the retrofit section.

If original, there is no low charge shut-off.

Just because it hasn't been run in years, doesn't mean it won't or can't be made to run.
 
Mine didn't have a schrader valve to check...

Hook the gauge hoses up before you warm up the car because you will get burned otherwise. You may have to wait till it cools down to remove them also. Like Jerry says, it get very hot quickly.
 
In addition to the vacuum test, a pressure test with nitrogen would be more conclusive in terms of finding leaks. You can rent a small bottle, or buy for less than $100 at a welding store. Vacuum only applies ~14 psi whereas with nitrogen you can charge the system to actual working pressures, prior to wasting that preciou$ R12.
 
I need to recharge my all original A/C system too. The last time I filled it the Freon leaked out within a month. I imagine that the 42 year old red hoses are most of the problem. I need to find a source to make new hoses, which unfortunately will not be red.
 
In many cases it is the seal in the compressor that has gone bad. We don't have o-rings in our cars.
Most shops use nitrogen to test and vacuum to prepare.
Plenty of how to instructions on the inter web. Key is to add as long as vent temps drop and stop when high and low sides start running up.
 
Not to plug my book, but...

...the single longest chapter in my book is on rejuvenating a/c in our old cars. I take you step-by-step through exactly what you're asking.
 
I just brought home a '72 Bavaria whose a/c, of course, was non-functional. Thought I'd use it to give a quick example here.

I hooked up the gauges to the low and high side fittings of the compressor. While screwing in the gauge fittings, I did NOT hear any gas escaping, so likely none in there. Then when the gauges were hooked up, they both read zero, so, correct, there was no gas in there.

I then attached a nitrogen bottle to the center tap of the gauges, fed it about 40 PSI, and opened up the red and blue taps to feed nitrogen to the system. I immediately heard the nitrogen escaping, indicating a major leak. I sprayed around the compressor hoses with Big Blu (industrial a/c leak detection fluid; didn't mention in my book; works amazingly well). Didn't see any bubbles, though. Odd.

So I took a length of hose and put it to my ear and hunted with the other end for the source of the sound. Just as SF Don said, the leak is from the compressor shaft seal.

So, compressor is junk, no surprise there. No need to do anything else before replacing the compressor. Then, as they say, lather, rinse, repeat.

The smart way to do it, as I say in the book, is to look the beast in the face and say "might as well do it once, do it right, and replace every one of these 42 year old hoses" (meaning compressor and receiver/dryer and every hose). On cars this old, it's not unusual to have to replace nearly every major component (condensers, being in front of the radiator, are in the line of fire for stray stones, not to mention corrosion).

But every once in a while you get lucky, find one bad component, replace it, leak-test the system, it holds, and you're good for a season or more.

--Rob
 
Update on A/C questions

Here is what I did so far. Borrowed an AC vacuum pump from Autozone. Since the system I have is R12, I had to buy an adaptor kit so the gauges would fit on the low & high side fittings on the AC compressor. While the low side adaptor had a shrader valve, the high side adaptor did not. The pin on the red hose (high side) was not long enough to push in the shrader valve that is inbedded in the high side connection on the AC compressor. Hope this makes sense.

I assume there is a schrader valve inside the low side of the compressor. Is this correct? If so, I have to further assume that the schrader valve of the R12 to R134 adaptor pushes in the schrader valve of the low side fitting on the compressor when I screw in that adaptor.

The result is that I could only use the blue hose for the low side and perform a vacuum test. I'm not sure what the low side would do and hopefully is not critical in trying to find out if the AC is in working order for me to fill it up with R12. Once the low side connection from the pump was done, turned the pump on and everything seemed to go well. Then noticed oil coming out of the pump and stopped the evacuation.

It turns out that the gauge connection to the low side of the AC compressor was not secured properly. The oil was coming out of the vacuum pump. My knuckles and arms are bloodied and black & blue from reaching the low side fitting of the compressor. I had to reach from under the manifold.

Thinking the pump was faulty I got another one from Autozone. Once I made sure the connection of the gauge to the low side fitting of the compressor was correct, (again, the low side only) I turned on the pump and left it on for close to two hours. The reading on the gauge was about 26 inch per Merc. I could not get it to 28 and certainly not to 30. After a couple of hours, I shut the valve at the gauge for the low side and let it sit for over an hour. The needle stayed at 26 inch per Merc and did not move one millimeter.

I performed this procedure several times with the same results. The last time I let it sit overnight and the needle on the gauge still did not move. It was at 26 inch per Merc every time time. Only when I reopened the valve on the gauge did the reading jump to zero.

From this test I came to the conclusion that there is no leak in the compressor, the hoses, connections or anywhere else. Am I correct in this assessment?

My next step in to charge the system with R12. I have three cans. One contains R12, oil, leak detector and leak sealer. The other two cans are straight R12. Any comments or opinions?
 

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Vacuum it one more time, turn off the gauges, hook up the can of freon to the center hose, let a little bleed out to clear the hose, and fill it up. I'd use the 2 regular cans first then if you need more go to the leak can, dont put that stuff in unless you need it. Or find a 3rd can of straight r12
 
Encountered problems

OK. I filed the AC system with one can of r12 and one can of r12 with oil, dye and sealer. Everything seemed to work.

The blower (squirrel cage) was on high and turning fine. All of a sudden, the squirrel fan wen't turning. Then noticed fuse #8 had blown. Replaced it, turn the fan on high and again the fuse blew. Tried 4 times with the same result and gave up.

I had not touched any wires, relays etc which I thought could cause this problem. Checked all connections to switches and relays and everything seems in order.

I then replaced the white fuse for a red fuse. Turn the AC on high and I can turn the fan with my fingers albeit there is some resistance. If the AC switch is off, then trying to turn those fans with my fingers is met with more resistance.

I then disconnected the AC switch and connected the blower fan directly to the battery. When I then used my fingers to turns those fans, the motor engaged and the fans were turning very slowly and then stopped again.

I then noticed some smoke coming from somewhere behind the evaporator unit.

Some months ago I had another thread where I explained the fans were not turning at first but did after some manual help. I had also explained that the ceramic part of that switch was getting very hot.

I had changed that switch with a working one and the blower was working fine until now and now I'm getting the same problem.

I'm trying to avoid the PITA of removing the entire evaporator unit to open it up.

Any idea as to what the problem could be? ANy help would be appreciated.
 
Sounds like the squirrel cage motor is drawing lots of amps and blowing the fuse. Likely due to age/wear. Sounds to me like you'll need to replace the motor unless there is something physically stuck in a blade or something but unlikely. Maybe once out it can be rebuilt.
 
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