Help Me Troubleshoot R134a A/C

[Ahheck01]

Just picked up an Mtech1 325is that had the R134a A/C conversion. The belt is new and turning the pully, but when I hit the A/C button in the cab, I don't feel anything kicking in, nor does it sound like anything is happening in the engine bay with the hood open. Also, the air gets neither colder nor hotter. I have no clue what to do. I want to make sure it's trying to run before I recharge it...

Suggestions?


Also, if I may be so bold as to put two questions in one thread - I'm picking up another 325i sedan (89) this weekend that needs an A/C recharge (but it's OE) - how hard is that to do? How is it done?

Thanks,

-Evan

[Trystym]

Ugh...could be almost anything - check electrical first, make sure that the AC compressor pump is getting power (fuses and relay - sorry my bentley isn't handy so I can't tell you which ones). I will assume that the AC clutch isn't turning (look at the front of the compressor, there is a plate on the front of the pulley - if it turns, the compressor is working, if not, the pulley is freewheeling.

Okay, I am outside looking at mine now - behind the right side headlights is the filter/dryer. There should be a small sight glass in the top and two hoses that connect to it - one goes in front of the radiator, the other runs to the firewall. Everyone that I have ever seen needs the glass cleaned off so that you can see through it, but with the compressor running you should see bubbles in the window. If not, you are most likely low on refrigerant. If the R-134 conversion was done correctly, then chances are that you just need to refill the system. Connect the can to the LOW side port ( on mine it is sitting in front of the right side shock tower) the can should not be able to connect to the other port - but I have heard stories of people trying to do it. Follow directions on the back of the can. When there is enough pressure on the system, you should hear the compressor clutch engage (an extra whirring sound) and the engine will most likely drop RPMs for a second. If you get and entire can in without hearing this (be sure the AC button is on in the car) then you have a leak.

As for question #2 - R-12 (OE refrigerant) is next to impossible to buy in the US - you have to be a licensed dealer. If you can find a place to get it (I believe it can be purcased in Mexico but I haven't ever looked) you will need a set of R-12 fill hoses, other than that, it is about the same as R-134. My suggestion is go to an AC mechanic for this one, he will either charge the R-12 for you, or else convert to R-134. (134 is getting to be the cheaper option now.)

Trystym - who is not an AC mechanic, but has a father-in-law that has beat this into his head over the years.:p

[Ahheck01]

What an amazingly helpful post! Thanks, and welcome to r3v!

-Evan

[Trystym]

There is at least one more test that might be possible. If you can find a way to apply 12V to the compressor clutch you should be able to see it move. You could theoretically do this with the car off, though at least on my 91 cab, I can't find a good place to open that circuit. The Bentley manual should be able to tell you where you can get at this. That would tell you for sure that the compressor is good. From there it is just a matter of having a sealed system and the proper amount of oil and refrigerant.

Hope this helps - life without AC is beastly.

[winstontj]

I heard from a dude in Autozone that you have to vacuum the old system to get out the old oil. Supposedly the old and new oils aren't compatable and can turn to toothpaste if you don't pull out all the old before putting in the new. I'm going to convert my system so I'd love to learn more such as ratio or amount of oil needed in the system, etc. I own a vacuum pump so I'll just hook it up at some point and suck out all the old crap and drain/flush the system myself. Seems like it still may be best for the pros to do though.

[ahheck09]

Ugh...could be almost anything - check electrical first, make sure that the AC compressor pump is getting power (fuses and relay - sorry my bentley isn't handy so I can't tell you which ones). I will assume that the AC clutch isn't turning (look at the front of the compressor, there is a plate on the front of the pulley - if it turns, the compressor is working, if not, the pulley is freewheeling.

alright we checked if the plate in front of the pulley was moving and it was not (the one with the bolts in it etc.) and according to you that means the pulley is freewheeling. what now?

[ahheck09]

anyone?