Hi,

Has anyone come up with a way to test the fusible link without removing the cabinet?

Thanks,

Raymond

Sent from my iPhone

> On Jun 6, 2015, at 11:58 PM, David Beierl <dbeierl@ATTGLOBAL.NET> wrote:
> 
> I just had occasion to trace out the A/C circuitry for '89-up and was
> rather dismayed at what I found.  There is unfortunate interaction
> between the A/C wiring and the vehicle wiring.  Tl;dr: I suggest
> putting  indicators on that will warn if S1, S42, or S23 should blow.
> as they can back-feed each other through the radiator switch and the
> mid-speed fan resistor when the A/C is operating.
> 
> '89-up, the A/C switch gets power from fuse S12 which also powers the
> heater blower. That fuse is supplied by the X line in the panel which
> is the output of the load reduction relay and is powered when
> ignition is on but you are not cranking.
> 
> That switch supplies the first two A/C blower speeds directly. When
> you switch to the third speed it activates one of the two internal
> relays in the A/C double relay, which is sourced from 50 amp fuse S23
> coming directly from alternator B+.
> 
> When you switch to speed four, it activates the evap blower relay
> which feeds the blowers directly without any intervening resistors.
> This relay is also sourced from S23.
> 
> If the other side of the A/C relay is not activated (next post) these
> are the only connections.
> 
> The A/C switch also powers the A/C thermostat. When the balance of
> the thermostat setting and the temp sensor II (not the one on the
> engine) calls for it, the thermostat activates the other side of the A/C relay.
> 
> This closes two circuits. The first one supplies power to the
> normally-closed side of the A/C pressure switch, thence through the
> normally-closed ambient temperature switch and the normally-closed
> A/C clutch relay to engage the compressor clutch (and incidentally
> inform the idle stab controller that compressor is engaged).
> 
> The second circuit connects S23 to the normally-open side of the A/C
> pressure switch. When the pressure switch operates, this section
> activates the stage II radiator fan relay (position 5 in the
> fuse/relay panel) which runs the fan at mid-speed; and the other
> section dumps the compressor clutch.
> 
> The second circuit also connects S23 to the low-speed end of the
> radiator fan resistor, which causes the fan to run at low speed. And
> here is where it gets tricky. Any time the first-stage switch in the
> radiator is closed (first stage nominal 95C, second (really third
> because of the stage II relay) stage 102C) it cross-connects S23 with
> 30-amp S1 through the radiator switch which is not meant to handle
> thirty amps. So supposing that S23 were blown, for example, its
> functions would be supplied with reduced overload capacity by S1
> through the poor groaning radiator switch.
> 
> And when the radiator 102C switch closes, it dumps the compressor by
> activating the A/C clutch relay, and activates the radiator cooling
> fan stage III relay, powering the radiator fan directly from fifty
> amp S42. And at the same time adding yet another cross-connection,
> back-feeding S23 and S1 through the mid-speed section of the fan resistor.
> 
> So there is a great deal that can happen that should not if S23 is
> blown (that should be the unhoused fusible link in the back somewhere
> on a relay board -- left pillar?), always supposing that one or both
> radiator switches are closed.
> 
> 
> Yours,
> David
> 
> --
> David Beierl -- dbeierl@attglobal.net