Cadillac Repair: a/c, E47, a/c compressor fuse

Question
Hello Bill   I have a 1988 Sedan Deville 4.5 and i am having a issue with the a/c blowing the fuse when i turn it on.  It usally will blow the fuse immediatly after the compressor engages, but sometimes it will run for awhile before it blows.  I checked the onboard diagnostic and had a e47 code but i cant seem to find a e47 code for that year of cadillac.  Just so that you know i also had an issue this past winter with the a/c compressor engaging when i ran the heat on AUTO(which would also blow the fuse)but heat worked fine when ran on ECON(i don't think the compressor engages on ECON).  I had an issue 2 summers ago with the compressor blowing the fuse at which time i replaced the clutch in the compressor and it had worked fine untill this summer.  Any advice would be greatly appreciated. Thanks

Answer
Hi Dave,

     Lets take these issues one at a time. With the E47 it means that the ECM couldn't communicate with the BCM. It could be a faulty ECM, BCM, wireing, connector or someone doing some testing and forgot to clear the code. What I would do is clear the code and see if it comes back. You could also check the connectors to make sure they are pushed and locked into the respective computors. Then should the code come back then dig in and do some further testing.
    
     When you push the auto mode on the climate control it doesn't matter what temperature you set the inside to be the a/c compressor should engage. However when the outside temps get below 60 degrees that is when the computor doesn't allow the compressor to run. It might be as low as 55 degrees but as a rule 60 is supposed to be the turn off point.

     Now for the fuse blowing problem I wouldn't rule out the compressor coil even though you had a replacement installed. It could have failed. In the wire harness at the compressor clutch connector there is an anti-spikeing diode. It only allows currect to flow in one direction so that the relays or electronics aren't subjected to high voltage spikes as the clutch engages or disengages. You will need to locate the diode and remove one leg from the wire in order to test it. One thing I do to test the circuit is to take a headlight bulb and and useing jumper wires and correct size terminals install it in place of the compressor after unplugging it. When you push the auto button the light should turn on and econ should make the light turn off. If the fuse doesn't blow after 5-10 tries then the circuit should be good. The exception would be you still need to test the diode. And the compressor or clutch are suspect. If the fuse blows then you would need to trace the wire harness to see where the problem is.

      Hope that helps. Bill