240 Late model / R134a A/C for 240s - what components were changed from R12?

Following on from @carnut222's yellow 245 build, it was mentioned in the thread how that latter--day 240 air conditioning systems were more efficient. This leads me to ask some questions from those with experience.

What parts are different besides the condenser?

Was there a change of evaporator unit (inside the cabin)?

If so, how is it different from the R12 units?

Can an R12 condenser be used with R134a with reasonable expectations?

If the evaporators are different, I'll be on the hunt for a couple of 240 R134a evaporators.

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Comments

  • Based on looking at it, the heater box with evaporator is somewhat different on the 2 93s I've pulled apart compared to the earlier ones, so I'd say the evaporator is different. The condenser is also different, as is the piping, orifice valve setup (I think?) and receiver-dryer (much larger silver unit up in the engine bay opposite side from the brake booster). I don't know WHAT the differences are, or what contributes to the changes in performance...would be interesting to compare earlier and later bits (the 91-92-93 bits all look very similar but only 93 had R134a from the factory).

  • seals are different between r12 and r134a. due to gas composition.

  • edited September 17

    Did a bit more digging about this.

    From YM91, the system in 240s was changed to a clutch-cycling orifice tube (CCOT) system. The condenser was also changed to a more efficient design. Also, the MCOMBU-type HVAC units were changed to accommodate a physically larger evaporator than earlier MCOMBU heater boxes.

    This photo from Cleanframetrap on TB shows the new type of evaporator, in LHD config.


    This other photo from Cleanflametrap shows an evaporator from the factory's R134a retrofit kit for pre-91 systems - note how it is a lot physically smaller.

    Given that LHD retrofit R134a evaporators for pre-91 cars are now unobtanium, it's expected that factory RHD ones are equally as rare. It would be nice to know what could be used as an alternative to the factory kit evaporator.

  • jamesincJames @jamesinc Oz Volvo Ice Fortress

    I can answer this, I've done a bunch of R134a questions. You can use the R12 system in its entirety with great results but you will want to change the dryer and the TX valve (you can use the same spec components as original just fine). You'll also want to fit an overpressure switch if one isn't present, and a small pusher fan in the front of the condenser to ensure your head pressures don't get too high. You'll also want to replace the oil in your system with an R134a-compatible oil, you can usually get it good enough by just flushing the oil out of the compressor and putting in new oil.

    I have an '81 system retrofit with an R134a compressor from a '92 MY (rest of system original), a '77 with a modern compressor and condenser, and another '77 with a full OE system with a rebuilt York 210 compressor running R134a.

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