Richard Eldridge wrote:
"I would prefer to not pay $200 labor to have this done. "
Good evening, Richard --
Try again on the labor -- it's about $560 -- labor only -- on a 124 like yours -- at a low $70 per hour flat rate. It's at least an 8 hour job and every element should be replaced at that time, including the hidden one tucked inside the HVAC box. Also, you would want to ensure *prior* to this job that you do not have a leaking evaporator (another known problem on 124s in the south).
This is a job that is unfortunately quite common in hotter climates and is rarely seen in cooler areas. A naive purchaser of a pre-owned 124 (300E, 300CE, 300TE, 400E, 500E) could *easily* spend upwards of $5000 or more on a non-functioning A/C if you have the "big 3" on 124 HVAC systems -- all known problems -- vacuum troubles, a leaking evaporator, and a Nippondenso compressor that has gone south (see the archive for "black death").
Someone early in this thread suggested the use of diaphrams *only* when experiencing vacuum problems with a 124. I would strongly caution against doing that -- there's simply too much labor involved -- DIY or not -- to *not* put new vacuum elements in the car. On a 123 or 126, different story, but a 124, I wouldn't put anything else in but new complete elements.
Also, someone mentioned a PPI by a certified technician for $100 and suggested that this should ensure that faulty diaphrams be discovered on the PPI. Unless that certified technician is a MB specialist, they probably don't have a clue how the MB HVAC system works.
Finally, a cheap test to check the function of your recirculation flap is to do a before/after test checking temperatures at the center vents under controlled conditions. In the after test, completely cover your air intake (under the wiper) with duct tape (the aluminum tape type). You'll know by the feel of the interior if the duct tape demonstrates that your recirculation flap was not working . . .