A/C - Dashboard warning lights

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TonyTT - 04 Sep 2005 22:43 GMT

On my 1990 Volvo 740GL the A/C compressor cycles about every 10 to 30
seconds, when the a/c clutch kicks in, the dashboard warning lights flash,
the a/c compressor clutch releases and in a few seconds it happens again.
Any ideas on what to check or replace?

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James Sweet - 04 Sep 2005 23:39 GMT

> On my 1990 Volvo 740GL the A/C compressor cycles about every 10 to 30
> seconds, when the a/c clutch kicks in, the dashboard warning lights flash,
> the a/c compressor clutch releases and in a few seconds it happens again.
> Any ideas on what to check or replace?

Check the harmonic ballancer on the engine, the alternator, A/C and other
accessories are all driven off the outer pully and IIRC this is attached to
the crankshaft through a rubber layer which breaks down over time. My guess
is the compressor is loading that down, causing it to slow and slowing the
alternator as well which is causing the warning lights to go on.

If the compressor still cycles then you're probably low on refrigerant.

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Mike F - 06 Sep 2005 15:13 GMT

There's a diode on the wire going to the compressor that's supposed to
suppress these inductive voltage spikes as the compressor switches on
and off. It sounds like that diode may be bad. Look for a little epoxy
box on the wire, grounded through one of the mounting bolts.

Also if your compressor switches on and off so frequently, it's probably
low on refrigerant.

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Mike F.
Thornhill (near Toronto), Ont.

Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)

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