19 August 2016

Refreshing the Air Conditioning HVAC A/C AC



The AC stopped working in the car.  It had worked sort of OK when I bought it, but it pretty much went to no cooling shortly after Schuh Syndikat.  One way to fix this would be to just add Freon and hope for the best.  But, the car is 18 years old at this point and it’s not getting any younger.  And, I wanted to learn how to do the work anyway.  I chose to replace the common failure parts.  Buying carefully-picked aftermarket ones, and this service isn’t too expensive.  I think pros would charge a FORTUNE for this sort of work but it really isn’t too hard.  I had the center console out anyway and that made it easier.  The parts I chose look identical to OEM BMW ones, and it many cases, they were exactly identical.  The one clue I did physically see that was probably a leak in my system was the hose between the compressor and the condenser was wet with PAG compressor oil.  That is/was the likely leak for me.  

I replaced every single o-ring in the system.  I replaced the evaporator, and I did have to bend the input and output tubes to match the shape of the original evaporator.  I did that using a very wide gauge screwdriver, inserted into the tubes.  And I bent them very slow and carefully.  I did replace the OEM foam around the evaporator with new, closed-cell foam.  I figure someone put that there for a reason, so I replicated it.

The connections at the firewall between the double pipe (which is inside the cabin) and the hoses, were tough.  BMW uses a steel locating pin inside the flanged connection to help locate the hoses and line up the o-rings.  But, the double pipe and the hardlines in the engine bay are aluminum.  2 dissimilar metals means galvanic corrosion.  I used a long thin flat head screwdriver as a chisel to break the connection loose.  There is not a lot of room there.

I did notice that several of the connections had not just an o-ring, but also a small plastic fitting that snapped onto the end of the male parts of the tubes.  I made sure not to lose any of these and I put them all back in place.  You need to take great care with this mod to line up every connection, make sure the o-rings don’t get pinched or roll, and hand start every bolt.  This is not easy to do!  Access is poor in most cases.

I did lube all o-rings with PAG 100 compressor oil.  I did add 1.5 ounces of PAG oil because I replaced the expansion valve, the drier, the evaporator, and one line.  TIS shows how much oil to add depending on what you replace.

I did have very bad luck with the Harbor Freight AC manifold gauge set I used.  I failed the leak-down vacuum test many times, and after I gave up and just decided to add R143A with UV dye, discovered the failed leak-down test was because the Harbor Freight low pressure side hose was leaking.  I got a new unit from HF, but it seems to leak too depending on hose orientation.  You get what you pay for, and this tool was only $59.  In hindsight, you need a quality manifold tool with o-ring seals.  The HF tool has semi-hard clear plastic washers to make the seals.  Not OK.  A better way to go would be to spend $159 and get a Snap-On AC manifold with o-ring seals.  I think I got the correct weight of freon into the car, but there is a chance the manifold tool leaked some and I am a little low.  Chances are some month when I have $159 burning a hole in my pocket I will get another, proper manifold tool and reload the freon so I can sleep better.  The AC is quite cold right now however.

Special thanks to Brent Williams and the Brent Williams Vocational School of Florida for teaching me some basics and some tricks necessary to do this work.

Freon, R134A, Dupont, need 3 12-ounce cans, $9.99r each
Receiver Drier (E36) - Rein 64538375754, $32.99r
Expansion Valve - OEM Rein CRP-ACX0101P, $23.99r
Evaporator - Rein 64518398840, $93.99r
A/C System O-Ring and Gasket Kit - Santech MT2640, $11.99r
Hose Assembly (Z3 328i 323i) - OEM Rein CRP-ACH0125P, BMW part number 64538363444, $9.29r
Schrader valve, 64509177577, $12.38r
Schrader valve, 64509177579, $12.38r

Total cost of this mod = $226.98r
Total investment in vehicle to date = $11915.23r


New parts: o-ring kit (left) and new shrader valves.

PAG 100 compressor oil and new expansion valve

Old evaporator, removed from car.  Delicious bits from 17 years of service.


Connection to the double-pipe at the firewall.  Note the steel locating pins.

Comparison of old versus new expansion valve.  The part numbers show different, but they are physically identical and substitutes for one another according to FCP Euro.

New versus old evaporator cores.  Note the orientation of the expansion valves is different.  I had to bend the tubing on the new one to match the old unit.

I did find compressor oil (wetness) on the hose between the condenser and the compressor.  I replaced this hose, which retails for $157 from BMW with an identical part that did not come in a BMW box for $9 from FCP Euro.

Hose part number

Hose comparison.  Not sure if the numbers are dates for the rubber.  Seems like they might be.

New drier

Leak in the manifold tool at the low pressure connection.  Fantastic.

Another leak in the manifold tool

When adding freon, you can put the cans into a warm water bath.  This will help the freon boil off and make its way into the system.

Freon fill specs.

This is how much I theoretically put into my system after vacuuming it out.  But, I think I actually have less than this because even the second manifold seemed to leak a little.

Weighing the freon before and after.

Ambient conditions in my garage at time of filling

After freon filled.

Evaporator and expansion valve sealed back into the airbox in the cabin.  I used metal HVAC tape over closed cell foam to replicate the seal the factory used.

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