Just take your time and if it seems that it is offering some resistance look around and see if there is something else attached. Don't forget to remove the a/c connection and heater hose connection.

Oh yea, at least on the 95 E300, there is a fastener on the bottom of the hvac box that you will need to remove prior to pulling the box out. The ones at the firewall are evident, the one on the bottom is only if you look for it.

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Jim