1989 E24 Dual A/C rebuild log

[gskrills]

I have officially finished my A/C rebuild after starting 7 months ago. I received most of my info and tips from this forum so I figured I would pay it forward and write out my rebuild log to help the ones who come after me.

Car:
1989 635Csi with Front and Rear A/C
195k Miles

Background:
I am a Mechanical Engineer with a specialty in thermal dynamics but I have no previous work experience on HVAC repair.

Original A/C had a sticker on it saying it was retrofitted to R134a back in 1994 but the compressor wasn't changed and the low and high side hookups were still for R12. The car spent its life in California and I bought and shipped it to Houston, Tx. The A/C worked successfully for my first year of ownership. Eventually, the front A/C started blowing warm while the rear AC would still blow cold, then eventually both stopped blowing cold.

I took it to my local shop (ABR Houston) and they said it was empty of refrigerant and had a leak. They couldn't determine if it was R12 or R134a. They quoted me $3k to find and repair the leak, retrofit to r134a, replace both TXVs (thermostatic expansion valves), and replace the leaky component. I declined and decided to tackle the job myself. This proved to be the correct path as the A/C needed a complete overhaul that would of cost over $5k to have a shop do.

My goal was to find the leak and convert to an efficient R134a system in the process. This would include a new aftermarket compressor, parallel flow condenser, new fan, and a new drier, at the minimum.

Tear Down

Engine Bay:
Unscrewed the lines from the original compressor, the condenser, and the drier. Come to find out, the large nuts on the A/C hoses are not because of the massive torque required but because of the diameter of tube required for proper A/C function. The A/C hoses are sealed using O-rings and the hoses are not actually torqued very high. If I had to guess, its around 20-25 ft-lbs for all connections. The condenser had a bunch of surface rust on the interior of the tubes indicative of moisture contamination over its 30 year life. In its current state it would not have been reusable as rust was just falling out of it. I also ended up replacing the regulating valve (PN 64511380659, most likely misnamed as 'Voltage Regulator') that regulates the rear and front AC suction line pressures in order to prevent backflow from one evap to another.

Rear AC:
The rear AC is much easier to remove than the front AC so I started with the rear in hopes of finding the leak. Remove the seats and center console and you find the rear evaporator assembly. At this point I made sure to ziploc bag and label all of my screws as the project got bigger and I knew I would forget where each screw went. This ended up being a lifesaver. My rear evap looked to have been replaced once and generally in good condition but one of the solder joints connecting the small discharge tubes to the evaporator looked to have corroded and began leaking oil+dye and the residue remained in the general area of the evaporator / TXV. I removed the TXV and evaporator together and found the TXV to be filled with dried gunk and it looked to have been stuck in a certain position, no longer correctly regulating flow. I put a new rear evaporator and TXV on the list of parts.

The rear AC lines under the passenger seat contain a muffler and a solenoid valve inline on the discharge side. Both of these parts are NLA so try not to break them. The muffler is a passive component that can be removed if necessary. The solenoid valve is an active part that is controlled via the rear AC controls. It will open or close the discharge line as necessary to provide cooling. Through my rebuild process, I have found out that the solenoid valve is a simple device and is serviceable / repairable so if yours is broken, don't throw it out! Details on the repair process are in this thread below.

At this point I noticed that the inside of my A/C lines were filled with surface rust / corrosion that would inevitably cause more corrosion / fall off into the refrigerant stream once I rebuilt the system. The rust would likely cause lots of problems down the road so I knew I had to get rid of it. During the rebuild process I took the car to get the lines flushed ($85) which removed large debris but the surface rust still remained.

Eventually I discovered every line in the system had some sort of inner surface rust. I decided to purchase new lines for the ones that were still available from the OEM (and weren't overly costly). For the lines that were too costly / NLA, I removed them from the car (including the 10 foot lines running to the rear AC) and removed the rust from them by using a product called Evapo-Rust (available at Lowes / amazon). I was able to soak the lines in evapo-rust for about 24 hours and all of the rust was removed with the fluid. I then flushed the lines with denatured alcohol to get rid of any remaining fluid / to dry the lines. I cannot recommend Evapo-Rust enough, it is truly an amazing product.

Front AC:
Remove center console, left and right lower dash, and radio/dash area to get at the front evaporator / fan housing combo. This was a horrendous job that I don't wish on anyone. I managed to complete all repairs without removing the upper dash, I feel like it might have made the repair slightly easier, but only slightly.

Upon removal of the front evaporator assembly, I found the counterweighted flappers (PN 64501376016) to have trouble functioning. The housing it was in had warped over time and caused the flappers to stick. This whole flapper and housing are NLA and are very fragile. In attempts to fix mine, I broke one of the flappers. I had access to a 3D printer so I tried replicating the part but to no avail, the part is just very hard to replicate as it is a counterbalanced flapper. I managed to fix the original flapper and upgrade the housing so that it should survive for years to come. If you have an interest in seeing the repairs let me know.

The evaporator looked pretty beat up, definitely original. The TXV looked ok. I didn't see any evident leaks but I replaced them both anyway for fear of rust contamination. At this point I was already in too deep to not buy new. The front evap is still available OEM (dual AC evap PN 64511375781) for around $500 out of germany with about a 6 week lead time.

Rebuild

Engine Bay:
Parts:
-Compressor:
Sanden SD5H14 (508 style) from summit racing. We all know this part is the go to replacement for e24 compressors. For this, I got the compressor bracket mounting kit from bimmerforums user demetk. These worked well for a start on mounting the compressor but in the end it required a lot more work to get it right at a professional level. Unlike other users on this forum, I decided to mount the compressor with the suction and discharge ports facing towards the front passenger wheel well. The compressor is allowed to be mounted with the ports facing 9, 12, or 3 o'clock, and the 3 o'clock position was going to allow for easier compressor mounting as well as easier line routing to and from the compressor. The original OEM compressor mounts to the engine via an M8 (8mm) bolt, and an M8 bolt on the tensioner bracket. the Sanden compressor mounting points are for 3/8" (9.525mm), so slightly larger. If you were to try and mount the Sanden compressor to the engine mount with an M8 bolt, the Sanden compressor would jiggle around because the 3/8" thru holes are too big for the M8 bolt. To fix this, I bought some metal bolt liners to shrink the Sanden 3/8" thru hole to fit an M8 bolt (McMaster PN 97305A200). The original M8 top bolt was too short to fit the new Sanden compressor so I had to source some 120mm M8 bolts (McMaster PN 91280A567) to fit. I test fitted the compressor, the mounting brackets, and the tensioner bracket onto the car and filled the gaps in between the bolt heads / nuts with washers. Once I had it mocked up correctly, I counted the number of washers for each section, took them off, measured their stack up height, and put together some dimensions to get aluminum shims made. You don't want to use just the washers as they have the propensity to shift under vibration. All in all, the shims cost me around $125. Let me know if you want more details on this.

-Condenser:
16 x 18 Parallel flow condenser from Nostalgic AC (PN 44-1618). The compressor needed custom mounting brackets to fit the OEM location so I salvaged the top bracket from the old condenser and had a machine shop mount it to the top of the condenser. I personally machined and built the bottom brackets for the condenser. If I had to do it again, I would take the old condenser and the new condenser to a shop and have them match the mounting points. The fabrication work cost me about $70.

-Fan:
Spal 14in fan with 4 mounting brackets (fan PN SPU-IX-30100382, brackets PN SPU-IX-30130011) from Summit Racing. I mounted the fan onto the new condenser and salvaged the original fan's power resistor and cable harness. The power resistor is used to run the fan at 2 different power levels depending on the HVAC load. I recommend using the resistor on the new fan if possible. Using the fan without the resistor could have unintended consequences on the overall power draw of the HVAC system.

-Lines:
One of the last things I did was get custom lines fabricated. I only needed 3 custom lines: One that ran from the underside of the 'voltage regulator' to the suction port of the compressor, discharge of compressor to top of condenser, and bottom of condenser to the drier inlet. I recommend getting everything else done in the car before custom lines, that way the shop can build the lines, hook them up, and pull a vacuum and check for leaks. You don't want to hook up lines to your drier and then leave those lines open to the atmosphere. The desiccant in the drier will be used up and become ineffective.

-Other Parts:
New 'voltage regulator' (PN 64511380659), drier (PN 64531466318 for dual AC cars), pressure switch (PN 64538363859).

Rear AC:
Parts:
-Evaporator:
OEM BWM Evaporator from ECS Tuning (long lead time) (PN 64501380571)

-TXV:
Egelhof rear A/C Expansion valve (PN 64501377051)

-Solenoid (PN 64511385418):
My solenoid was working when I took it out of the car. I cleaned it without taking it apart and checked its function on the bench top and it was still working. Once reinstalling and charging with refrigerant, it was non-functioning. I had to source a new one from a craigslist part out for $150. Once I had a replacement part, I took my old one and tore it down in attempts to repair it. Inside the solenoid is an electromagnet and a pipe. Inside the pipe is a spring and a metallic plunger. When the electromagnet has power applied to it, it forces the plunger against the spring and leaves a small space for the refrigerant to flow. With power off, the spring forces the plunger back into place, not allowing the flow of refrigerant. There are very few parts to the solenoid. I cleaned the parts, reassembled, and bench top tested. My original solenoid is now in working order for whenever the other one fails.

Front AC:
Parts:
-Evaporator:
OEM BMW Evaporator from ECS Tuning (long lead time) (PN 64511375781). This comes with that black gooey 'Cork Tape' to go around the suction line / TXV bulb to prevent condensation. This stuff is not my favorite to work with so I opted for foam wrap. Both are not very easy to get off after installation.

-TXV:
OEM TXV (PN 64501380658) from Pelican Parts. The sensing bulb on the TXV should be attached to the suction line on the outlet of the evaporator with the supplied screw clamp. This should then be insulated after installation. The sensing bulb is there to measure the temperature of the refrigerant on the evaporator outlet to adjust the flow of refrigerant to get the correct evaporator superheat.

-Insulation:
There was quite a bit of deteriorated foam insulation on the evaporator box housing and the associated counterbalanced flapper housing. I cleaned the housing with Goo Gone and denatured alcohol and then used compressible open cell foam (from Lowe's/Home Depot) in the places where the foam should have been. This seals the evaporator box so that there are fewer leaks into the dash board area. My car and its dash had warped slightly over the years so the foam did a great job in picking up the inaccuracies between component mates.

When putting everything back together, I kept blowing a fuse related to the AC. Come to find out, the transistor (PN 64111381785) which sits inside the evaporator box housing is sitting at 12V and it touches the evaporator, it will likely ground out.. Great design guys. The transistor is in the box because when it is on it warms up so I'm thinking they stuck it in there to keep it cool. I put some kapton tape around the edges to prevent further shorts and I was good to go.

Closing Everything Up:
Use new O-rings on every connection you make. There are quite a few different O-rings in this system. Off the top of my head I can think of the suction lines, the discharge lines, the drier connections, the muffler connections, the 'voltage regulator' pressure sensing line (small one). They all have different o-ring sizes. Before you order a part, check to see if it needs a specific o-ring. If it does, order 3 of them (or more), whats a couple extra dollars for having to potentially halt your project because you don't have the o-ring you need.

Order yourself a bottle of Nylog Blue Gasket and Thread Sealant. This is the oil we use to coat the o-rings as well as the threads of the connections to prevent leaks. Don't use any other oil on your connections or gaskets.

A/C and PAG Oil:
The Sanden SD5H14 comes from Summit Racing prefilled with 175 cc's of PAG oil. The service manual states to only use Sanden SP15 oil to add to your system. I don't know enough about it to know whether or not you can use a different brand of oil. Sanden's service manual recommends 3.3-8% ratio of oil to refrigerant by weight. The badge on the inner hood of the car stated that it used 3.69 lbs of R12 in 1989.

pulling this data from another thread:
R12 - 120.91 g/mol
R134a - 102.03 g/mol -> 84% weight of R12
R152 - 66.05 g/mol - 55% weight of R12

Many automotive HVAC repairs have listed 80% of the R12 weight as the norm for R134a weight. Due to the fact that the compressor and condenser are not OEM anymore, the total amount required is going to be in the ballpark of 80% of 3.69 lbs, or ~3lbs (48 oz), or 4, 12 oz cans of refrigerant. Remember, this is ounces of weight, not volume (oz vs. fl oz). Based upon this, we should have somewhere between 1.584 oz and 3.84 oz of oil in the system. Due to our system being Dual A/C and there being quite a few nooks and cranny's for this oil to sit (rear AC muffler, long rear AC lines, 2 evaporators) I would try to err on the high side of this value. The specific gravity of the SP15 oil is 1.02 so we need approximately 3.92 fl oz of oil (116 cc's) in our system. But why then, did our compressor come with 175cc's of oil in it?? I'm not sure... I guess Sanden wants to err on the side of safety when shipping their compressors. I ended up not adding any extra oil to the system. Adding oil to an A/C system, as well as adding refrigerant seems to be more of a skill than a science, where too much oil is better than too little, and too little refrigerant is better than too much.

Refrigerant Charging:
I bought 4, 12 oz cans of pure 134a without any oil, stop leak, or dye additives. If you want to add dye, do it during the charging process. I rented a manifold gauge set and vacuum pump from Autozone (free rental as long as you return it). I had added R134a conversion fittings to the 'voltage regulator' (low side) and the drier (high side) at some point.

I watched some youtube videos on how to pull a vacuum using the pump and manifold gauge, pulled a vacuum for about an hour and let it sit for 24 hours. I didn't have any leaks showing up so I proceeded to hook up my first can of refrigerant, purge the line with refrigerant so you aren't adding air to your A/C, and started filling on the low side fitting. I emptied the first 12oz can, hooked up the 2nd 12 oz can and began continuing to fill. For this can and the next, I forgot to purge the line (60"?). I remembered this in the middle of the night after filling the system. The next day I called up a shop and asked about the risks and they said don't worry about it. I heard that the air gets trapped at the top of the condenser and reduces condenser effectiveness but I'm not an expert here. Let me know if you know something different.

I started taking pressure measurements after the 2nd can (24 oz).
T ambient: 75-80F
24oz:
Ps - 30 psig
Pd - 160 psig

36oz:
Ps - 36 psig
Pd - 210 psig

~42 oz:
Ps - 36 psig
Pd - 210 psig

At this point I stopped adding refrigerant. I had attempted to do some evaporator subcooling / compressor superheat measurements with an IR thermometer but they were inaccurate due to the measurement area being large (1" square from 12 in. away). I reset and got some thermocouples and a thermometer from work the next day. I redid the test and recorded temperatures to measure condenser subcooling.

T ambient - 75F
Suction Pressure - 37 psig
Suction Saturation Temp - 41 F
Discharge Pressure - 200 psig
Discharge Saturation Temp - 130 F
Compressor Outlet Temp - 131 F
Condenser Outlet Temp - 120 F
Compressor Inlet Temp - 48 F
Rear Evaporator Inlet Temp - 104 F
Rear Evaporator Outlet Temp - 50 F

Condenser Subcooling is the degree to which the fluid is below it's saturation point.
Condenser Subcooling = Discharge Sat. Temp - Condenser Outlet Temp = 130-120 F = 10 F.
This seems a little low, I was shooting for 12-15F but I doubt I know how to get it much closer.

Evaporator Superheat is the degree to which the fluid is above its saturation point.
Evaporator Superheat = Evaporator Outlet Temp - Suction Saturation Temp = 9 F.
This also seems a little low, its possible that a very small amount of liquid is making it back to the compressor. With TXV systems, the TXV self adjusts to let a certain amount of refrigerant through to a preset superheat value set by the design of the TXV valve. What that value is, I'm not sure, it is probably anywhere from 10-20F of superheat. You should not adjust your charge based upon evaporator superheat with a TXV system.

The final temperatures I am getting out of the vents is between 45 and 50F, more on the high side when I run both front and rear A/Cs. I feel pretty good about where the system is at, it might be just slightly overcharged (maybe keep it at 36oz / 2.25 lbs instead of 42?) but I don't think I'll adjust anything for now.

Total Repair Costs:
Time: 7 months, during weekends and afternoons. I would say close to 80hrs.
Money: $3,257

Let me know if you have any questions or want specific pictures of the set up!

[ytr1903]

Great write up! You may have inspired me to do my dual a/c system. Emphasis on "may". Seriously, though, thanks for the time it took for your coverage of the project.

[jeffcfp1]

Very nice write up. You make a great point concerning the rust on the inside of the lines. Let me add to this thread that the missing piece of the puzzle for cold front vents isn't just the replacement of the front expansion valve but the "Regulator" on the fender well. It clogs just like the expansion valves, however, unlike the valves is very easy to take apart and clean. I'm running basically the same setup (Sanden/Spal fan, no Parallel Condenser - but for comparison purposes getting 40 degree temps from front vents. Sure is nice to have working a/c in these cars!

[ramp]

That is one incredible project. Haven't tested my A/C yet this year.

[JimPA]

Terrific writeup. Patience, coupled with more patience and thoroughness, seem key. I probably spent that much at two shops trying to achieve working a/c in my last M6 but never succeeded.

[ramp]

Well the A/C no longer pushes cool air. What to do. Too hot to even think about it right now.