Auto A/C Refurb

[88E30M50]

I'm working on getting an old '98 BMW 3 series back to daily driver status and the A/C is the next item on the list to restore to working order. When I plug an A/C manifold set in, I'm getting a slightly higher reading pressure when static on the high side. Low is about 89psi and high is showing 100psi. Running, the low side does not change and the high side barely changes and it does look like the clutch is engaged and compressor turning. The system was flat when I started, so I pulled a vacuum on it for about 30 minutes and it held pressure for another 30 minutes, so the system seems tight.

Right now, I'm thinking that the compressor is shot. Question is, should I replace the expansion valve at the same time? I'm thinking that I should, since if the compressor is shot, there's a good chance that debris might be blocking the EV. That could be the reason behind the offset static pressures. I hate getting into the dash area unless needed though, but unless I'm wrong, I think that it's needed. It adds less than $50 to the cost and a few hours of work.

 

[rhamersley]

I'm working on getting an old '98 BMW 3 series back to daily driver status and the A/C is the next item on the list to restore to working order. When I plug an A/C manifold set in, I'm getting a slightly higher reading pressure when static on the high side. Low is about 89psi and high is showing 100psi. Running, the low side does not change and the high side barely changes and it does look like the clutch is engaged and compressor turning. The system was flat when I started, so I pulled a vacuum on it for about 30 minutes and it held pressure for another 30 minutes, so the system seems tight.

Right now, I'm thinking that the compressor is shot. Question is, should I replace the expansion valve at the same time? I'm thinking that I should, since if the compressor is shot, there's a good chance that debris might be blocking the EV. That could be the reason behind the offset static pressures. I hate getting into the dash area unless needed though, but unless I'm wrong, I think that it's needed. It adds less than $50 to the cost and a few hours of work.

Never went that far with it, but when my former Tahoe blew the compressor, I changed the compressor and the accumulator under the hood. Along with that there was a screen in the line going to the accumulator that was full of oil/debris...it fit into the inlet of the accum. If I recall, my orifice was under the hood and I just took it out and blew it out.

 

[indyblue]

I just did this last spring on my 2001 Sonoma. I got a rock auto kit for under 400 bucks included pre-oiled compressor, condenser, accumulator/drier, O-rings for the connections and a new orifice.

I got AutoZone loaners for the vacuum pump, refrigerant manifold and the valve for the refrigerant cans.
It took a couple afternoons to swap everything out and recharge but the system works well now.

 

[Ark]

If the clutch is definitely engaging and the compressor turning and you see almost no pressure differential, it's probably toast. Blocked systems will pressure spike and then kick the compressor off.

Always replace the accumulator/dryer when you crack a system open. That's what it's there for, it's your filter. When compressors go boom they often puke debris into the system that ends up in the accumulator.

As for the expansion valve, it's a moving part so it's good to replace while you can unless it's totally unfeasible. Replace any o ring you take apart. Pull vacuum on it again to leak test when finished, recharge with refrigerant and oil.

I killed an EV by gunking it up with parts store refrigerant once. The pressure differential thing might be because the valve closes when not running and it doesn't quite leak across the valve and compressor to absolute equilibrium. I'm sure its an expensive part on a BMW, but my attitude towards opening an AC system is to make sure I never have to do it again.

 

[88E30M50]

Thanks guys. I have the manifold set and a nice vacuum pump and have returned several old cars to life before. I was just on the fence about the EV but it makes sense to crack the system open once and just do it right instead of being half-fast about it. Parts are really not too bad price wise and I think that a new compressor, acumulator/dryer and EV should be less than $500. Cool air in a 26 year old car though... priceless.