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air condition

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I have a problem.   When I turn on my A/C, either on hi or norm, the fuse blows for the blower/speedo/a/c circuit.  So i did some experimenting: I purchased  about a dozen 20 amp fuses and tried with the a/c wires not even plugged into the compressor....It will still blow...

This plug on the compressor can be removed and the fuse still blows. So I know it is not the compressor.  When I put it on just blower vent or heat, the fuse does not blow.  I put it on A/C and it blows again.  I have tracked the two wires that go to the compressor up to the firewall where it joins many other wires in the covered harness. No signs of breaks in the coating.  So, i started thinking about the a/c relay but do not know where it is located.  

This is the relay i bought.  but don't know where to plug it in.

Anyone have any ideas as to why my fuse keeps blowing when i slide the controls to AC?  And where is the relay located.

It is a 91 sub  w/ rear a/c.  The rear a/c blower is on a different circuit because it still works when the fuse for the a/c blows.


Edited by: SgtDel at: 5/21/06 7:42 pm

Del,  the light green and dark green wires going to the pressure switch on the desicant container, have you tried disconnecting them? dont remember if the ac will turn on or not if it is disconnected, but that switch may be shorting out to ground.  i believe dark green wire is a/c request which hooks to the pcm (tbi, right?) to bump up the idle, light green should be to the switch in dash.  just a thought, I'll grab my book out of the garage tomorrow for the diagrams.  
BTW your truck my not have a relay,  my 86 does not have one since (not so sure about the 94)the votage to engage the clutch is minimal,  there is only one large power wire which goes the the silver box on the blower case, and then it splits from there to the fan motor etc.

Cooltoolguy, You brought up some good ideas.  If i pull the wires from the pressure switch the clutch will not engage, but that may help me diagnose where a problem is (will see if fuses still blow w/ ac on.  Yeah, my 91 is a tbi.  

And come to think about it, the idle DOES NOT increase like i think it should when AC is on.  In fact, it seems as though the rpms of the engine are barely turning the ac compressor, i kind of get a roaring sound from the compressor when engine is idling and ac is on. That is when the ac was working, up until last week.

I am going to try tomorrow to unplug the blower resistor and see if i can further limit some possibilities.  The blower does work well w/ the heater and vent, just breaks fuses when ac is on.

I'll also unplug the pressure switch and then switch to ac and see if she breaks a fuse then.

That would make sense if I don't have an ac relay.  I know the blower has a relay for high on top the evaporator box.  I think those are the other wires that plug to that gizmo on top the box.



Del, I think you got the blower relay. It sounds to me like the AC switch itself would be a good place to look. From there the problem lies from the switch to the load in the ckt. So pop the switch out ...


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