Are you sure the part is bad? That part is not made any more. I only found one broker who claims to have some. They will likely want a lot of money for it.

The part has thermal protection built in and will shut itself down if it gets too hot. You might try putting a little heatsink on it. If it keeps running hot then the solder joints will fail over time. Heat in a linear regulator is just a matter of (Vin-Vout)*current. Any regulator new or old will get just as hot. So even if you replace it put a heatsink on it. A piece of copper or aluminum will work. The glue shown there is likely a type of RTV to protect from vibration.

Mike

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

That part is a lm7805. It is very common and can be had for a few dollars.

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I got too many cars!! Insurance eats me alive. Dave

78 Corvette Stingray - 3k
82 242 Turbo Volvo - Manual - 270k
86 300e 5 speed manual - 210k
87 420sel - 240k
89 560sl - 78k
91 420sel - 205k
91 560sel - 85k
94 GMC Suburban - 90k
97 Harley Davidson Heritage Softail - 25k
00 GMC Silverado 1 ton 30k

That regulator can be replaced by dozens of 5 volt low dropout regulators. I use an LM2940T-5.0 made by National Semiconductor with a rating of 1 amp (the original was 0.8 amp) - about $1.50.

I would definitely put a heat sink on this integrated circuit. It runs very hot without one - seems to be a design flaw instead of a component failure.

There are slip on heat sinks available from electronic supply houses. You need to know that the component package is called TO220. If you have any silicone grease use a small amount between the regulator and the heat sink - it gives better heat transfer. Put a small dab of silicone rubber between the heat sink and one of the nearby capacitors (220uF electrolytic) to protect the IC from vibration.
Use good quality electronic grade solder when installing the regulator.

While you have it apart, resolder the push button switch connections as well - the connections often crack from stresses.

You might as well change the bulbs while you have it apart if you haven't already.

Good luck!

Was the discoloration on the back of the circuit board already there?

If so you might think of getting the number of the part ( I'm guessing an SCR or Triac, but it is probable all DC so an SCR) so if it burns itself up you'll know the part number. The tab on top is for a heat disapation and the hole is to add a larger heat sink if needed.

If the part got hot enough to unsolder itself and or discolor the circuit board you might consider adding a heat sink.

Thanks guys for the info!
Yes, Noel, the discoloration was already there when I took the board out.
I will happily replace the part, but the reason why it failed or is overheating concerns me.
Could it be another componant that is drawing too much current?
What does that regulator regulate??
The aircon works... then turns itself off... blower and all... and then you get heat from the center and screen vents. Sometimes you can get it working by pushing the defrost button and the pushing the AC again.

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2009 Mercedes ML320 Bluetec

That regulator IC brings the 12 volt supply down to a stable clean 5 volts that the microprocessor and other chips on the circuit board need to operate.
I have repaired dozens of these and have not had one come back after putting a heat sink on the regulator, so I do not believe that there are other components in the circuit that are drawing too much current.