82 380 SL question

[Steve Aufderhei]

I own an 8000 mile original 380SL. The A/C just started acting up. Previously, the A/C worked fine... it has never been recharged or worked on. Now when I activate the A/C the vents blow hot air! I shut the unit off and restart. Initially, it would restart and blow cold. Then gradually it stopped the cold air and blew nothing but hot. If I advance the thermostat wheel to a hot temp, and then reset it to "min", the unit will restart cold again!

Is the problem as simple as the thermostat? For a nominal fee, it appears I can replace the entire A/C Control Assy for a reasonable price (rebuilt unit). How do I determine the problem? I live in an area where there are no qualified MB shops for about 60 miles.

Thanks

[Steve Aufderhei]

My 380SL is an 8000 mile original car. The A/C system has never been worked on nor recharged. Up to now the unit has cooled perfectly. Recently it started blowing hot air when activated. For a few days, shutting it down and simply restarting, restarted the cooling. In the past couple of days, that no longer works, and it continues to blow hot even though the thermostat is set at "min". If I advance the thermostat to a hot temp, and then reset to "min", the A/C starts cooling perfectly again. I can find a rebuilt A/C Control Assy rebuilt for a reasonable price. Should I simply replace it, or could there be another problem? I live 60 miles from the nearest MB dealer, and would prefer to have a local mechanic handle this, if it is this easy.

Thanks,

[300sdToronto]

Wow, only 8,000 miles? Like to swop??

Before you opt to replace the CCU I'd suggest checking the monovalve as it sounds like you are getting excess heat that is competing with your AC system's ouput.

It would be helpful to know if you are getting HEATED (as opposed to ambient) air if the CCU is on the economy setting.

There are lots of posts (especially on the diesel forum) on how to check and if necessary replace the monovalve. It is easy to find on the firewall, on the RHS of the engine compartment. (referring to the RHS when sitting in the vehicle facing forwards). If the diaphragm on the monovalve is torn or the electrical plug is loose then heated water will be released into the heater core at all settings .....

If the monovalve is OK then you may have an AC clutch problem or a CCU issue.

[UT_Tech]

If your car is really an 1982 model then you probably have an ACCII system with a servo. Later models have the ACCIII system which uses a monovalve.

You can sometimes "tickle" the system back into working by unplugging the connector on the outside air temp sensor to force the servo to full heat. Unfortunately the usual cause is a bad servo or servo amp which would leave you no choice but to replace both.