AC keeps blowing the fuse...

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ikeepmychevytoo

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Hi... this is a typical GM from '84 with DA-6 AC compressor (if matters). In April it started to blow the fuse, however if works, it blows cold. This just get more often in the following month and now whenenever AC is turned on voltage needle drops promptly then fuse blows in the same instance. Battery was weak (12.4 volts prior to cranking)which replaced today, cranks much better but AC fuse behaves the same.

Is this a typical problem? Some mechanics want to rebuild the compressor, others says it may just be low on oil, none of the operations are cheap however. I've inspected the shop manual throughly and found no troubleshooting for this one. Why would fuse blow? ...as if the compressor is working with electricity. I've shorted cycling sensor no change. At random, if it operates it is cyling in/out normally, blows cold and de-humidifies. However there is a noise inside the car, like the usual "line" sounds of some big old fridge (two-stroke engined boat on a distant waterfall). Not sure if this sound is new, or it is me that trying to find some culprit.

This Monday I'm going to get one more idea from another shop specializing on ACs. I just would like to know if there is any logic in that a faulty compressor or one that low on oil could blow the fuse but just not seize. Isn't it supposed to be mechanical driven?
 
quote:
Originally posted by JHZR2:
I had this happen in my MB when the clutch went bad. Blew a 35A fuse!

JMH
Click to expand...
I would assume you mean the ac clutch. Ohm it out and see what you get. Check the coil to ground too.
see if you can freely turn the compressor. Have to turn the center part not the pully. It shuld have some resisteance but not alot.

Ken
 
The coils that activate the clutch are probably bad. Their are other issues as well though like the control head and the blower motor if tied to the same fuse? The control head is low current so that is not likely but a blower motor could cause issues? Check the obvious things first!
 
quote:
Originally posted by Ken42:


JMH
Click to expand...
I would assume you mean the ac clutch. Ohm it out and see what you get. Check the coil to ground too.
see if you can freely turn the compressor. Have to turn the center part not the pully. It shuld have some resisteance but not alot.

Ken [/QB][/QUOTE]

Thanks but I just replaced the whole thing, compressor and clutch. Problem solved and cold AC once again!

JMH
 
Thanks for the replies... I'll look closer to the tcc loom, it was tangling... never thought of that!
I've already checked the blover and its relay. As far as I know there is blower motor, a horn and nothing else shared within the same fuse. There is a diode in the clutch, I'm also suspecting it...

So I guess consensus is no need to recharge just to see what happens...

thanks again
 
Here's an update...

I found the culprit. It was the power steering cut-out switch which interrupts the compressor when the steering demand is high. The connection was grounding to the speed governors case. However I have the system re-charged since a mechanic "thinks" the pressure was already low. I'm happy since there was nothing costly so far.

Now compressor starts and works OK, but after 15mins of driving causes an increased load then this load is varying, I feel it at steady speeds. Is compressor seizing? Could it be low on oil? What would you guys think?

I have it charged three times in six years and no one added oil ever. Do I need to add oil? Compressor backside is oily so definitely there is some oil loss, although it can keep the charge more than a couple years.
 
how rapidly does it cycle? If the pressure was too high the hi pressure cutoff would shut it down. Once the pressure is down, it will start again. start-stop-start-stop. A low pressure situation can cause almost the same reaction.

unless it's a pretty rapid cycling (like less than 30 seconds on), I think it's normal. the compressor will sap a huge amount of power. you can feel it on almost any car, especially a 4 cylinder at steady speed.

If it does this after 15 minutes of cooling, i think that it is normal since once the car is cool and you turn the fan to low, pressure can rise causing the same cycling.
 
Just a quickie: Some had a small diode near the harness connector at the AC clutch (anti spike diode). Sometimes this diode goes south and shorts. If your clutch ohms OK, look here next.
 
Thanks all for your interest and replies...

mechtech and kenw,

Previous charge was on duty for more than five years and performance wasn't too bad when it was charged just two years ago. So last one probably unneeded. I heard the clutch yesterday when I was driving along a long wall, indeed it was kicking in and out with lesser periods than 30 secs! On highway it somewhat dragged too much so I've turned it off before the belt squeals.

Your comments are probably right on and explaining what the mechs have been skipping here. They have been too ignorant to elaborate sypmtoms, now I'll find the specs and only ask for checking pressure.
 
Boy, thats a science.
Its a combination of ambient temp, ambient humidity, output temp, low pressure/high pressure in relationships to each other.
Another way is to have the system evacuated, then filled with the exact charge by weight.

1984? Is this an R-12 system?
 
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