Just a brief follow-up to our earlier correspondence. We jumped #2 to #10 on the cooling fan control but, no change. In looking at the electrical schematics we did notice that the A/C Pressure Switch wasn't grounded but, grounding that line (#5 in connector A14) made no difference. Looking at the 3 connectors to the rear of the A/C control (A12, A13 & A14) the charts imply 2 power leads to connector A12 (#1 & #15), one ground to connector A12 (#7) and one ground lead to connector A14 (#5). These are all engaged per spec. But, the control unit is still dead. This result is consistent even though we replaced the cooling fan control, A/C control unit and Temp./Radio switch with others that came from vehicles where the system was working. We are able to control the heating/cooling fan by jumping the Heater Relay (using a rheostat to adjust RPM). Same for rear window defroster with a toggle switch. It should be possible to control the servo motors with a toggle switch and the A/C output with some form of thermostat. I mention circumventing the Automatic Climate Control because we have installed an older reworked Chevy 5.7L V8 with a six speed double over drive manual into this 1992 Lexus SC400 (we call it a "Chevus"); meaning, we are applying 1960's technology to a 1990's style vehicle (no computer, no FI - just a Holley 750, etc.). Accordingly, some things have changed. Everything works regardless of which drive train is installed but, for some unknown reason the A/C control is dead. I should add that although the original A/C compressor and system have remained intact, the compressor is not yet electrically attached but, it doesn't seem that the lack of this component should cause the remainder of the HVAC system to fail. Or, are we missing something? We noticed that the A/C compressor's connection has three leads whereas the clutch probably only needs two leads (a + and a -) to be engaged. Can you explain the third lead? Also, if we convert the system to manual HVAC controls (we have already installed a manual heater control valve for the heater core) can you recommend a Toyota vehicle(s) from which we could obtain a suitable (manual) temperature control for this A/C unit? Have a good day.
Monday, November 16th, 2015 AT 2:57 PM