Re: A/C goes flakey with "low pressure" cut-off

[Chris Newbold <cnewbold@transarc.com>]

"R. Cummings" wrote:

> I'm not familiar with the 93 90 system specifically, but I'm going to assume
> it is a TXV (Thermal Expansion Valve) system as opposed to the GM orifice

I don't really have any further info, so I'll assume you're right. The only
other thing I do know is that is uses a "variable displacement" compressor.

> The yellow connector switch is a high pressure switch that closes at 190
> psig and switches the engine cooling/condenser fan to high speed.

Ah. That would explain why the contacts in the yellow connector were looking
burnt; all that fan cycling!

> The low pressure switch is located on suction line just after it exits the
> evaporator case.

Ah! One thing I have noticed is that when the compressor cuts back in again,
it's preceded by a "pop" or "click", sort of like a relay but not quite,
from deep in the bowels of the center console...

> I would be surprised that the system cycles at high load and not low load. I
> would expect it to cycle at low ambient, low blower speed, high compressor
> rpm on the low pressure switch. The reason for this is that when the

Well, some of it fits, some of it doesn't: The blower speed is usually
on the low side (less than 1/2 speed), compressor RPM is high, and there
is high airflow at the condenser ( ~80MPH :-).

> Are you sure it is cycling on the low pressure switch? The first thing to do

That's what the ECU says it is :-) It's got this neat little graphic which
will show you the reason why it shut the compressor down...

Thanks for your insight, Bob. Maybe I'll tear into the console and see if
I can find the low pressure switch. Can this be replaced without discharging
the system?

-Chris