Air conditioning question - blower fan intermittent

[Wade Nelson]

My AC (blower fan) has taken to cutting in and out.

Is there a controller / circuit board "between" the fan speed control knob and the blower fan itself that gives it the variable speed?

Is it prone to failure?

The compressor SEEMS to keep operating as air coming out of the vents, even when the blower isn't spinning, is still chilled.

[Kurbycar32]

You dont mention what model car, this is my early 260 experience. I cant speak to the failure but there is a device inside the blower housing that looks like a set of resistors that control blower speed. Follow the wire back from your blower motor, it should connect to a Y type cable with one end going to the fan switch and one end going to the resistors. the resistor "panel" can be removed from the blower housing for inspection/cleaning. Mine was covered in ancient red antifreeze (most of the passenger side under the dash was) from some sort of tube bursting on a previous owner. I cleaned mine up with electrical cleaner and its worked since. That answers your question, i would still check fuses first.

[Wade Nelson]

A resistor pack is common with a blower that has 3 distinct speeds. The 280ZX has infinitely variable blower speed which USUALLY requires a "module" of some sort containing a power transistor. The knob on the dash is just a rheostat.

My query is posted in the S130 (280ZX) section of this website.

I suppose I'll have to drag out the schematics unless someone comes up with a common failure to look for. I've been battling one problem after another with this AC system for 2 months now. Every time I fix one....another starts occurring.

As for fuses, I've never seen an intermittent fuse. They're either good or blown, although I HAVE seen corroded fuse sockets / connectors.

[Wade Nelson]

Turns out your reply actually had some merit; instead of sticking a resistor pack up in the airstream they stick the cooling fins for the power transistor portion of the "amplifier" up in the airstream for cooling. I pulled mine down expecting it to be coated with leaves, grass, etc. but it was clean. The transistor DID look like it had gotten hot at some point... case was brownish

My guess is my problem is in the relay, since revving the motor (increasing voltage) made the AC kick back in one time. Higher voltage can sometimes arc through corrosion on relay contacts and re-establish contact.

I may also hardwire a DPDT "failsafe switch" to send 12V directly to the blower motor. bypassing the speed control completely ..when the other system kicks out. That way I can keep MY cool when it quits blowing halfway to the Z-car rally in Arizona... should spin a little faster too, since there's typically a .7V drop through ANY transistor based speed control --

meaning the fan is "seeing" 11.3 max instead of 12.0 like it would if wired directly.

Well, I just pulled down the relay, swapped it actually, and dissected the old one...

And THERE IT IS. Right on the contacts is a tiny hi spot where metal has transferred from one contact to the other over time, preventing full and complete contact. That little "whisker" will also get oxidized over time and become non-conductive, unless the contacts are pure gold. Probably not, on a Datsun.

The solution? An emery file or emery cloth to burnish the contacts a little.

So there it is, a 15 minute fix to an intermittent blower fan.

Edited August 1, 2012 by Wade Nelson