Nissan Sentra B14 AC or Electrical Problem

[acupalypse]

Hi Folks,

Since I bought my pre-owned sentra (B14) in 2003, I have been experiencing AC issue, i.e. compressor clutch disengages prematurely esp. when stuck in traffic or idling the car with AC on for a long time, hence causing the RPM to rise to ~1800. Then after a while (about 4-8mins), magnetic clutch will engage all by itself again. Now it's 2010, i'm still using the car and the problem still exists, considering over the past 7 years, i've almost checked and replaced every AC part suggested by 4 different AC shops (including a Nissan Dealer) - compressor (x3), condenser, filter, expansion valve, thermostat, aux fan motor, fan blades, evaporator and other cleaning services. What's left to be replaced are high pressure cut-off switch, relay, AC dial knob, electrical wire/connectors and aluminum tubes. But i'm not replacing/checking any of these anytime soon as I don't feel there's something wrong with any of them

Anyways, last week my battery went dead and couldn't start the car. I found out that it was my mistake to replace the battery when I bought a new one and gone dead again after 3 days of using the car. I checked the alternator voltage reading (<12V) and it didn't look charging. So I replaced it with a surplus alternator. As I'm a bit skeptical whether everything is OK even after replacing batt and alternator, I frequently check voltage reading at the batt terminals using DVOM.

I'm a bit surprised when I did the check with car engine hot and AC is turned on, voltage drops gradually (~8-10 mins) from 13.75V to 13.08V. Headlights and stereo don't cause this much of voltage drop, let alone not gradual but instant drop of about ~0.2V. My suspect would be electrical components: magnetic coil, aux and rad fan motors, and AC blower motor. Turns out, looks like the aux and rad fan motors are causing the issue - with the AC off and engine idle for long, CTS (coolant temp sensor) senses high temp and turns on both fan motors and i took the reading.

So, I think that the cause of my AC clutch disengaging prematurely is voltage dropping too low for the magnetic coil to hold the clutch, especially if the AC is ON for a long time. My question - what could be wrong with my fan motors as they seem to eat up the voltages (probably too hot and the resistance drops (?)). Or is this a voltage issue to begin with?

Any ideas or similar experience? Need your expert advice pls

Thanks!

[Jakk]

Same problem with my series 3 sana may matulungan nyo po kami hirap kapag traffic at kainitan ng araw mamamatay aircon then tataas ang rpm to1800. Need you help mga guru..TIA.