All-

1985 300sd constantly blowing hot air. check fuzes to make sure these were good, they are (did this because I remember in my old 123 that if the ac fuze went, the system would blow hot air).

Also shot compressed air into the sensor in the Roof to clear out any other debris. Anything Else I should check?

Device just Forward of the Firewall with heater hoses and 2 wires.
(When they go bad,all you get is heat.)

You will be looking down on it,and see the Square Aluminum Plate with a screw at each corner and the Male electrical plug.

A repair kit is available (The Rubber Diaphragm usually ruptures).
Mercedes part # 114 721 30 07 [Second Picture]

Repair is: Gently disconnect the electrical plug ('remember it's 26 years old)
Remove the 4 Screws ('Careful not to drop,if you do, they're GONE)
Lift the Aluminum plate up and R+R the Insert.
'Button it all back up like they do in Sindelfingen and Bake Cookies in the
Passenger Cabin,OR NOT!

Your Heating system has a Bladder,Filled with Engine Temperature Coolant
under the Windshield that Prevents Frost/Freezing once the Coolant is
up to Operating Temperature.
(You can drive in Sleeting/Icing conditions and the Windshield will not "Frost".)

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'84 300SD sold
124.128

Before opening this thread, I thought the OP was saying the CCU was always hot. I immediately thought of some of the infernos described when the CCU shorts out to due a bad aux pump.

Scary stuff.

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'85 300TD "Puff The Magic Wagon" - Rolling Resto
'19 Mazda CX-9 Signature - Wife's sled
'21 Morgan 3-Wheeler P101 Edition
'95 E300d - SOLD
'84 300TD "Brown Betty" - Miss this one
'81 240D "China Baby" - Farm grocery getter

X2

Simple repair and fairly cheap.