Mercedes-Benz Forum banner

Mystery 400E A/C Issue

342 Views 6 Replies 3 Participants Last post by  tuttebenne
1993 400E. A/C will not come on for maybe 30 to 45 minutes of driving and the engine and engine compartment gets really hot. Sometimes it comes on by itself and other times I have to restart the engine. When it does come on, it blows normal and the air is cold. Almost sounds like the heat is causing expansion of something until contact is made and it starts working again. When engine cools down, no a/c until things heat up again. I'm lost on this one. Maybe it's a wiring issue, but all mechanics want to do is to rebuild the HVAC system which is costly. Any thoughts would be helpful.
1 - 2 of 7 Posts
There are a lot of basic checks that should be done, for example, the correct function of the low pressure switch on the reciever dryer, the engine temperature sensor, the amount of refrigerant in the system.

Aside from these, if you have an intermittent A/C system, you need to rule out the ignition switch as a possible cause. Also, consider that the system is designed to shut off the system when certain conditions exist. One of them is high engine temperature, another is a slow compressor due to a slipping serpentine belt.
The red switch is the high pressure switch. The one on the opposite side is for low pressure. If you jump the two wires from the low pressure switch together with a paper clip or suitable jumper, you will be telling the system there is enough refrigerant in the system and the compressor will start once you start the engine and select an A/C mode. If it does, then yes, you either have low refrigerant or a bad switch.
  • Like
Reactions: 1
1 - 2 of 7 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.