This article serves to provide nuanced detail for those looking to refresh their OEM setup (Denso with early style dryer in particular); one of the biggest roadblocks is that the OEM parts catalogue (ETK) is often wrong.
Also, reference to this article for how to recharge the AC system:
Leak Detection
For the do-it-yourself mechanic, the most effective method of finding leaks is by using a refrigerant leak detector.
Most leak detectors can measure a leak of approximately ±0.01 oz/month; less expensive units are less sensitive, and more expensive ones are more sensitive. To put this into perspective, a full R12 charge is 2.1 lb; that means the detector can find a leak that would take 280 years to fully drain a full charge—they are very sensitive.
The most common leak point on a Denso compressor is right between the clutch and compressor body. Its also very common to have a leak at the dryer sight glass.
E30 Compressor Types
The E30 was fitted with three types of AC compressors:
Denso 10P15E – This came as PN 64521386256 and PN 64521378387; both are completely interchangeable, the latter number is just an earlier production PN (’87). You may have to cut and crimp the 1-pin connector when getting a remanufactured compressor that goes to the AC clutch, as there were at least three different types of connectors used over the years.
Denso compressors are often remanufactured and sold without manifolds, as the expectation is that you swap yours to the new compressor.
Seiko Seiki – Various different models, but they are all essentially cheaper clones of the Bosch Wingcell.
Bosch Wingcell
Oil Types
There are three primary AC system oils: Mineral oil, Ester oil, and PAG oil.
R12, as the system was originally designed for, uses mineral oil, while R134a retrofits require Ester oil and PAG oil, as mineral oil is incompatible with HFC refrigerants (like R134a). PAG oil will not mix at all with mineral oil and is incompatible with the original AC seals meant for R12.
Ester oil is generally used as a retrofit oil as it can mix with mineral oil and PAG oil, and so requires much less aggressive system flushing.
*Hydrocarbon R12 replacements like R12A (also called HC-12) are compatible with all oil types, but generally, it’s best to stick with mineral oils if you plan to run R12A as Ester is 50 times more hygroscopic and PAG is 200 times more hygroscopic. This means that Ester and PAG absorb moisture much more easily and so require extra diligence in evacuating moisture before charging, and can cause internal corrosion.
Refrigerant Types
There are three options for E30s: R12, which is outlawed and increasingly hard to find (NOS recharge cans), R134a, or a drop-in hydrocarbon replacement like R12A (HC-12).
Hydrocarbon replacements are much more popular outside of the United States and can be purchased and charged without any kind of license. In Canada, for example, recharge kits are widely available at places like Walmart (Duracool), Canadian Tire (Red Tek), and Princess Auto (Ultracool). They are all essentially mixtures of propane and butane; hydrocarbon refrigerants are very efficient, and you can expect R12 or better performance. They require no change in O-ring material or oil type; they are direct drop-in replacements.
If you fear running a hydrocarbon replacement because it’s flammable, just remember it’s 16 oz of refrigerant, but you’re sitting on 55 liters of gasoline. Mercaptan is also often added (rotten egg smell) to detect any leaks, much like natural gas at your home.
Expansion Valve
Almost every expansion valve for sale today is stamped for R134a but can be used for R12/R134a/R12A as the factory E30 uses an evaporator freeze switch. The R134a expansion valve orifice is ever so slightly larger, which can let additional refrigerant through, meaning it will make the evaporator colder, but at the risk of freezing it. Luckily, the E30 is fitted with an evaporator freeze switch, so this is a non-issue as the freeze switch will turn the compressor off just before the evaporator freeze point. Many automakers like Mercedes-Benz just rate their expansion valves for R134a and stamp them as compatible with R12 also.
Evaporator
Many people forgo changing the evaporator and chase additional performance by way of parallel flow condensers. What most people don’t realize is that after 30+ years, the small gaps between the evaporator fins are almost always blocked by dust and dirt. This means the air from the blower fan is going around the evaporator instead of through it, and so a lot of cooling transfer is lost (what you feel at the vents).
Follow this on how to change the evaporator:
Receiver Dryer
It’s best practice to change the receiver dryer any time other work is performed on the AC system, not least because it’s common for the receiver dryer to develop a leak around the sight glass.
What’s not so nice is that not only were there three types of AC compressors, there were also at least three different types of receiver dryers. It mostly boils down to single and double switches; most early cars ran separate switches for low and high pressure, while later cars ran a single sensor.
There is plenty of information about single-switch dryer setups, but finding details around the double-switch setup is sparse. The below provides all of the part numbers needed for the dual switch setup:
One switch is NPT threaded (self-sealing) and requires no O-ring, while the other comes with an O-ring already fitted (not NPT).
Expected Performance:
This is referred to as Delta T. You can expect a 10°C difference between ambient and vent temperature at idle, a ~18°C delta at speed, and up to 20-22°C with recirculation on with the fan on high; R134a is slightly worse than R12 and R12A.
O-Rings and Valve Cores:
The AC system is designed with SAE-sized O-rings, and BMW converts these measurements into showing the ID of the O-ring.
The switches, dryer, and expansion valve normally come with O-rings already. But in the case of the Denso compressor, it’s best to purchase this O-ring kit as it provides the hose-to-manifold O-rings that normally are not provided with remanufactured AC compressors:
It’s best practice to replace the valve cores on the Denso AC compressor manifolds and the low and high-pressure Schrader valves. This can easily be done with a valve core removal tool and this valve core kit:
Most people do a vacuum and think they are leak-free, but forget that while doing a vacuum you won’t see leaks from the low and high side Schrader valves; replace them!
Tools
The AC hoses to the Denso AC compressor manifolds are 22mm and 27mm and can be removed (with the wrench at various angles) with a wrench of each size. It’s best to remove the hoses versus the four manifold bolts (6mm hex), because it will allow you to replace the hose O-rings and manifold Schrader valve cores.
The rest of the AC system is a mix of 17mm, 19mm, 21mm, and 24mm.
Oil Charge
Denso systems require 6.78 oz total system oil (200cc), while Bosch and Seiko require 10.15 oz (300cc). Oil can be added directly to the part you are changing (it’s for the benefit of the AC compressor but gets circulated everywhere).
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