New A/C Problem - melting fuses???

[mthomas58]

Paul, just sent you a PM

[rick-l]

Originally posted by mthomas58
OK, I just re-tested voltage across the fuse with one probe on the top bus and the other probe into the distribution wire just below the post.

Got dramatically different results of 0.13, so let me explain my meter settings. If I switch the probes I get a reading of -0.13

.

Was the fan running and the clutch pulled in?

2 watts isn't going to get that copper block too hot.

[scottb]

Mark: When you pulled the power for the fan assembly you're running on the rear condenser, where did you tap the power from?

[mthomas58]

Originally posted by scottb
Mark: When you pulled the power for the fan assembly you're running on the rear condenser, where did you tap the power from?

I'm pulling power for the condenser mounted fans from the engine fuse block #3 which is for the rear window defroster that I don't use because it no work.

[mthomas58]

Originally posted by scottb
Mark: When you pulled the power for the fan assembly you're running on the rear condenser, where did you tap the power from?

Like this.....ignore comments below diagram as it has been rewired (properly) per recommendation from mystertrain.

Anyway, I'm off to the dealership this AM to see what they can find.

Thanks all for your ideas and suggestions ( and to you electrical experts - thanks for your patience with me)

Will follow-up with what they find.

[mthomas58]

Problem Resolved: System had been overcharged causing the compressor to run at higher pressure & draw more amperage.

All electricals checked out OK. Dealer tech evacuated the system and then recharged with the proper amount of R-12.

He states that it is normal for the fuse block to get "warm" when the A/C is running full tilt, but it should not get "hot". Static pressure in system before he started was 80psi.

Thanks again for all your help!

[Jim Sims]

"Problem Resolved: System had been overcharged causing the compressor to run at higher pressure & draw more amperage."

??

The compressor clutch is an on/off device, it's current draw isn't modulated by compressor load or pressure. There is nothing electrical in the mechanical part of the compressor beyond the clutch. If there is too much load the clutch may merely slip which will make frictional heat which can heat up the clutch coil but this will increase resistance and cause current to decrease. Clutch slipping can also be caused by an incorrectly set magnetic gap.

Compressor was running continuously or too long (with clutch slipping insufficient compression was occuring) and thereby heating the circuit too long or all the time. Correcting the refrigerant charge level likely solved the slipping problem but perhaps other problems remain:

Running voltage is too high (car's voltage regulator failing?) and this causes excess current draw for fixed resistance items like the compressor clutch coil.

Clutch coil has a internal damage (shorting) and resistance is too low causing it to draw excessive current.

Clutch magnetic gap is excessive (or amp-turns in coil reduced due to shorting causing less magnetic field to be produced) thereby preventing sufficient clamping to occur causing the clutch to slip under high load.

[mthomas58]

Originally posted by Jim Sims
"Problem Resolved: System had been overcharged causing the compressor to run at higher pressure & draw more amperage."

??

Jim, .....my layman's interpretation.......thanks for the clarification!

[rick-l]

Originally posted by mthomas58
Problem Resolved: System had been overcharged causing the compressor to run at higher pressure & draw more amperage.

Someone better explain this to me

[derkpitt]

How can this statement from page3 be true?

"1) Disconnected power to A/C clutch and ran evap blower motor only -still heats up"

[Barrpete]

In my case it turned out to be a bad voltage regulator. I had the same melting fuse problem, but after a replacing the regulator and having the alternator rebuilt I have been running the AC constantly for over 2 weeks. Temps are up to 105 . No more melting fuses.

[mthomas58]

No more problems here after getting the system evacuated and recharged with the correct amount of R-12 at the dealership! Good thing.....humid 95 degrees yesterday!

[Sunroof]

"system recharged with R12 at the dealership" ?????

Mark...
Do you mean R134? The only place to get R12 is on the black market. Its as rare as King Tuts treasure!!!!! Since it was a dealership (Ellis, Hennessey) it had to be R134.

My 1973.5T has factory AC and years ago and I recall the AC fuse being as hot as hell, but never to a point of melting. Rather then putting in a new fuse block I installed an inline fuse and it has been working great since. I also replaced the older relay in the smugglers box with an updated unit. New barrier hoses, R134 and a fan switch and it runs cold in this Atlanta heat.

Glad to hear your worries are over, BUT if by chance you did find a way to get R12, please let us know your source!!

Bob
73.5T Sepia of course

[mthomas58]

Bob, definitely R-12. Shouldn't be too hard to find - just pricey. Wendt's shop did the overcharge (1 can R-12) and Jim Ellis did the evac and recharge with R-12....since I had too much in the system, I guess they came out ahead on product. Han's over at ******** has also got it.....he worked on my system last year and we went through two full charges before getting me back on the road "leak free".

BTW, Wendt charged $45.00 for 1 12 oz can. My father-in-law just gave me a couple of cans that he bought years ago at Kmart for $0.98 each! My how times have changed!

[Sunroof]

.....well shiver me timbers.......!!!!

I had Bob Sanderson a few years ago (before Peter took the shop) charge me up with R12 at great expense only to see the stuff run out the bottom low pressure hose that night. After replacing all the hoses with new barrier hose (Auto Cool in Smryna) and a new drier, I decided that R134 will have to suffice based on the R12 prices. So far it has been adequate for these hot temperatures, but Porsche AC systems have never been known to be really cold; just enough to keep the sweat to a minimum on sweltering days!

Glad to hear Mark that all is well on your AC now. Very informative thread.

Bob
73.5T Sepia

[pmax]

Originally Posted by fred cook

The fuse that you are having problems with powers (I think) both the evaporator fan and the front condensor fan. You need to check both fans to see if one of them is or has frozen up and is thus pulling too much load. Since this is the only fuse point for both circuits, you could have a wiring fire if the problem is not fixed! If you can't tell which fan is the problem, disconnect the condensor fan first (easiest to get to) and run the a/c. If it is the condensor fan, the fuse will be ok. If the problem is in the evaporator fan, the fuse will continue to melt. You also need to loosen the screws that holds the wiring to the fuse block and clean the corrosion off the wires and out of the hole in the block. A .22 caliber rifle wire cleaning brush is just the right size for the job. Use the brush and some spray electrical cleaner to get both the hole and the wires completely clean. If the two fans are ok, cleaning the connections may fix your "issue". Hope this helps.

Is that what happened here ?

Fs: 1982 911sc-$5000
quote: It ran fine before the air conditioner condenser fan shorted out and caught fire.