[ChrisCyprus]

Hello friends. I am struggling to find the problem with my smart 451. So to guide you a bit: As i was driving my car (with a/c on)lately suddenly i realized that the cluster went blank. It was showing nothing. Fuse #12 burnt. I changed it with a/c off and cluster was then fixed. When i turned a/c on again i faced the same again.cluster went dead.i took my car to 2 mechanics and 1 electritian and all told me that i should replaced my a/c compressor which i did,paid a fortune and the problem still exists. Anyone faced the same problem like me? I would be really grateful if anyone can help. Thanks in advance

 

[DudeInTheSmart]

Bad relay in the A/C system? A/C fan gone bad? Something in your A/C electronics is shorting or drawing too much current. Are you handy with a multi-meter? Is it running for a bit then dying, or dying as soon as you flip the A/C on?

 

[ChrisCyprus]

Bad relay in the A/C system? A/C fan gone bad? Something in your A/C electronics is shorting or drawing too much current. Are you handy with a multi-meter? Is it running for a bit then dying, or dying as soon as you flip the A/C on?

Thanks for your reply sir. Actually before replacing the a/c compressor as soon as i was switching on the a/c the cluster was dying. When i changed the compressor then for 20minutes the car was working good but then died again

 

[DudeInTheSmart]

OK, now I am starting to speculate a bit. If it runs for a while, then blows a fuse, it isn't a permanent short. I'm thinking the compressor was the core problem, as replacing it lets the system run for a while, but as it went it caused something else to strain or fail. If the fan motor is going bad (don't know if it is same circuit) it could pull too much current as it warms up and cause the fuse to blow. I don't have a wiring diagram, but it could be a relay that shorts once it heats up or similar. It sounds like it is something that is starting to strain after it has been running a while.

 

[DreamCarOwner]

It`s going to be tricky to track down. Had it been a short in the ac compressor clutch you would have lost fuse #14. You are losing fuse #12. Here is a list of what is on fuse #12:
Instrument cluster
Additional instruments (pod clock & pod tach)
Microwave sensor (car alarm interior sensor)
Rain sensor / light sensor (auto wipers)
Alarm siren with inclination sensor
Left turn signal lamps/brake light relay
Right turn signal lamps/brake light relay
Mirror heater relay
Automated manual transmission control unit
TPM [RDK] control unit
Combination switch
Cockpit switch group
Data link connector (ODB2 connector)
Starter-alternator control unit

Most of these control relays are inside the SAM (fuse box) mounted on circuit boards. Do you have access to a trouble code scanner that you could plug into the ODB2 port and see if there are any stored codes? It could be anything of the above things listed for fuse #12. But I don`t see a link between pushing the AC button that would affect any of the above listed things. Fuse #18 is also listed as an instrument cluster power source. If you have the tach and clock pods they connect to the instrument cluster.
The instrument cluster is a huge part of the CAN BUS system on the Smart. It coordinates signals from all the modules and controls your switches through the CAN BUS. When you push the AC button or turn on a turn signal or turn on headlight or wipers you are sending a low voltage signal over the CAN BUS to tell the SAM (fusebox) to flip on a relay to turn on the device. The 12 volt switching is done on the relays inside the SAM, the switch is merely a low voltage circuit to tell the SAM through CAN BUS to turn something on or off. That includes all the module communication like air bags, shift motors, clutch actuator, ABS brakes etc,... not trying to be confusing here but just trying to help you understand how complex this problem can turn out to be. It will take some testing to try and troubleshoot this. DCO

 

[ChrisCyprus]

It`s going to be tricky to track down. Had it been a short in the ac compressor clutch you would have lost fuse #14. You are losing fuse #12. Here is a list of what is on fuse #12:
Instrument cluster
Additional instruments (pod clock & pod tach)
Microwave sensor (car alarm interior sensor)
Rain sensor / light sensor (auto wipers)
Alarm siren with inclination sensor
Left turn signal lamps/brake light relay
Right turn signal lamps/brake light relay
Mirror heater relay
Automated manual transmission control unit
TPM [RDK] control unit
Combination switch
Cockpit switch group
Data link connector (ODB2 connector)
Starter-alternator control unit

Most of these control relays are inside the SAM (fuse box) mounted on circuit boards. Do you have access to a trouble code scanner that you could plug into the ODB2 port and see if there are any stored codes? It could be anything of the above things listed for fuse #12. But I don`t see a link between pushing the AC button that would affect any of the above listed things. Fuse #18 is also listed as an instrument cluster power source. If you have the tach and clock pods they connect to the instrument cluster.
The instrument cluster is a huge part of the CAN BUS system on the Smart. It coordinates signals from all the modules and controls your switches through the CAN BUS. When you push the AC button or turn on a turn signal or turn on headlight or wipers you are sending a low voltage signal over the CAN BUS to tell the SAM (fusebox) to flip on a relay to turn on the device. The 12 volt switching is done on the relays inside the SAM, the switch is merely a low voltage circuit to tell the SAM through CAN BUS to turn something on or off. That includes all the module communication like air bags, shift motors, clutch actuator, ABS brakes etc,... not trying to be confusing here but just trying to help you understand how complex this problem can turn out to be. It will take some testing to try and troubleshoot this. DCO

Dear friend i really appreciate all your effort to reply to me. Thank you very much!!!to all of you!!