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Can freon overcharge cause fuse to overheat and blow?

mthomas58 on Sun May 17, 2009 1:18 PM User is offline

Year: 1987
Make: Porsche
Model: 911
Engine Size: 3.2L
Refrigerant Type: 134a
Country of Origin: United States

Can a system overcharge lead to fuse overheating and blowing? If so why? Controversy on another forum on this issue. I had this problem 2 years ago after topping off my R12 charge. After troubleshooting by cleaning up the fuse block and wire connections did not solve the problem I took the car to the dealership. They said overcharging can create more load on the system and lead to the the electrical overheating issue. My plastic body bullet fuses were overheating and melting vs blowing the metal part of the fuse. Tech evacuated and recharged with the recommended qty of R12 and no further problems - period.

On other forums, it has been argued that there is no way coolant charge will affect electrical performance of the system. If this is not true, what is the technical explanation why?


Cussboy on Sun May 17, 2009 1:30 PM User is offline

On a 1970 VW with AC, I also experienced occasional fuse melting v. fuse blowing in an inline fuse. I purchased a new inline fuse holder and moved the 30 amp fuse into an area in the trunk that had a little more ventilation. I was in Arizona, figured underhood heat was one of the reasons.

mthomas58 on Sun May 17, 2009 2:09 PM User is offline

This is in a Porsche 911 and the fuse panel is in the front trunk away from the engine heat.

Cussboy on Sun May 17, 2009 4:37 PM User is offline

Originally posted by: mthomas58
This is in a Porsche 911 and the fuse panel is in the front trunk away from the engine heat.

That was my point: so was the 1970 VW.

tscaravan on Sun May 17, 2009 10:06 PM User is offline

Is your compressor driven by the engine or by an electric motor?

mk378 on Mon May 18, 2009 1:31 PM User is offline

Overcharging will not overload any of the electrical parts. The technical explanation is that the clutch coil just generates a magnetic field to pull the clutch plate in. The current does not vary with any mechanical operating condition.

Most likely you're going to have to replace the fuse box. After overheating once, the spring contacts that connect to the fuse have lost their temper. No amount of cleaning up or re-bending them will help. They will never make good contact with the fuse again.

bohica2xo on Mon May 18, 2009 2:00 PM User is offline

Ding Ding Ding We have a winner!

If the plastic body fuses are melting, the contacts are junk. Your best option is to replace the high current fuses with a new fuse block for real fuses.

I don't know why the square-heads stayed with the crappy fuse design for so long. Original fuse bodies were ceramic, and the clip tension was fairly high. That still did not address the lack of contact area with that fuse design. 20 (or more!) amps through a contact area of about .001mm just makes a heater. Then the plastic "bullet" colapses a little bit, the contact pressure goes down...

Bypass the OEM fuse block for the high current stuff, and use some standard automotive fuseholders.


"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

NickD on Mon May 18, 2009 4:14 PM User is offline

He is a semi-logical explanation, overcharge causes severe high pressure in the compressor that can cause the clutch to slip. In slipping it generates friction causes red hot heat that can actually burn the enamel insulation of the clutch coil causing a major short circuit. However, this is not reversible by recovering the refrigerant, once the coil is toast, it's toast and has to be replaced along with the rest of the clutch and the idler bearing as well, it's grease is also toast.

Have already seen this. With only minor slipping, the coil will get warm or even hot, and since copper has a positive temperature coefficient, it's resistance will increase decreasing the clutch coil load. That does not blow a fuse.

Queer electrons can also blow fuses.

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