Diagnose Inverter motor dirve - aircon unit

Jul 23, 2016 4 Replies

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Mr Sandman 9 years ago

Hi all,

I have an aircon unit that failed. Fault code 'PU' says the capacitor charging circuit failed, this is confirmed by checking the voltage at the three large electrolytic caps which show 43vdc, but oddly 85v ac. The expected voltage at the capacitors should be 180-380vac.

I am a low level electronics experience chap, so need some advice on how these caps would typically be charged.

They are used, as i understand it, to smooth the supply to the variable speed fan and compressor in the aircon unit.

Looking at the other test points on main pcb, everything else checks out ok.

Here is a link to the (large) manual for the aircon unit if any one fancies helping me out.

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Id apreciate any help/guidance,

Many thanks,

Steve

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Rheilly Phoull 9 years ago

You have worked through the logic of the trouble shooting guide for the charge failure ??

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Phil Allison 9 years ago

** Gobbledgook.

Large electros acquire *DC voltage* after being charged.

What sort of multimeter / voltmeter are you using ??

An old moving coil one by any chance - many of the latter read double voltage on the AC ranges compared to the DC ranges if mistakenly used for DC.

Reverse the probes and the reading drops to zero.

.... Phil

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Mr Sandman 9 years ago

** Gobbledgook.

Large electros acquire *DC voltage* after being charged.

What sort of multimeter / voltmeter are you using ??

An old moving coil one by any chance - many of the latter read double voltage on the AC ranges compared to the DC ranges if mistakenly used for DC.

Reverse the probes and the reading drops to zero.

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I am using a digital multimeter, a fairly decent one. Probing the caps directly i get the voltages i mentioned. is this showing ripple indication a bad capacitor rather than a bad charging component? the caps show no signs of leakage or expansion externally.

thanks for the help, sorry im a newbie, and dyslexic so may sound muddled.

cheers

steve

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Phil Allison 9 years ago

** Make and model - please !

** What about when you reverse the leads?

FYI:

There has got to be at least one DMM maker who uses a half wave rectifier directly coupled to the DC meter circuit - mimicking how an moving coil multi-meter does the same job.

... Phil

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