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Strange A/C - radio problem


Luke Skywalker
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My oldish nissan van has developed a strange problem. every time the A/C compressor kicks in (A/C clutch of course), the radio is re-starting. Now this isn't to shocking since the voltage is also dropping down to about 10v for a second and then coming back to around 13v.

any ideas welcome...


Great Pumpkin
Hi Yisrael. How old is "oldish"?

If the a/c compressor needs some lubrication, there could be an excess draw of current as the clutch kicks in.

And if the radio is an older digital system, a voltage drop could certainly "re-boot" the radio.

Just a thought.
Tom M.


Luke Skywalker
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"oldish" would be 14 in this case (yeah I know for a site dealing mostly with LBCs this isn't really old) The radio is probably old enough to be called "oldish" also.

You are talking about oil in the compressor? not some sort of lubrication of the clutch?

Deleted member 8987

If the AC clutch engaging drops voltage to 10, well, something else down the line is bad. The clutch fuse would blow or the clutch relay would smoke. You have a voltage feed issue, positive or ground. Where is the voltage measured when it drops to 10V?
Load test the battery, check the alternator output, voltage drop across cables under load, that kind of stuff.

Deleted member 8987

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If locked, your belt would squeal. Excessive load, same. Your clutch fuse would blow.
Compressors are oiled once, then when you open and drain the system, do it again. No dipstick.

10V where? Engine has to be running to engage A/C, so if 10V at battery, you have a charging system problem.

Do your headlights draw it down? Again, where are you measuring the 10V?

The battery will provide enough power to arc weld. Dirty cables? Still, 14+ off the alternator, not 13. Load like I said would blow the fuse if enough to drop three volts, E-IxR.

The more I think about this, especially since I had a clutch coil go bad this year....the maximum current to the clutch is small. Windings are small. Just enough to pull the plate in on compressor shaft (my winding opened when it got real hot outside...corrected when cold).

I think your alternator has a problem. Or the idle kick for the AC isn't working.

The load when the mechanical AC starts (not electrical) slows the engine down, drops your 13v charge off....and battery is probably shot, too (or not even getting enough charge) to not hold voltage up when the charge effectively goes away when idle drops.


Luke Skywalker
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I think you are on the correct track. If I recall correctly, I measures + on the battery and - on chassis so any resistance would have been measured.
Unfortunately I have been dealing with my own problems instead of the cars problems.. but will get back to this very soon since it has gotten hot out again.

This is a nice torquey diesel and doesn't seem to have any problem keeping idle speed up, and the alternator is on a different belt so it slipping shouldn't be an issue.

The other issue that may be is the big radiator fans (it has 2) but I think problem there big enough to drop voltage would blow the fuse.

I think the first thing I need to do is go back and remeasure voltage at battery and then start tracing the wiring. I think you are 100% on with a bad connection somewhere.


Luke Skywalker
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Problem found! and as predicted by TOC a voltage feed issue. The bolt holding the ground cable to the chassis was rusty, loose and impossible to get at.
I guess I could have tried tightening it if I took out the radiator and more stuff. Just broke off the old bolt and found a new mounting place for the cable. Kind of surprised it worked at all. that cable connector was just flapping around. Must have sent out a stream of sparks every time we started the engine.
Checked voltages both at battery and a few other locations, voltage is now at ~13.5 at idle with EVERYTHING on.. Radio no longer resets itself.
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