What’s up, I have had this issue for a few months now and I’ve weaved my way through almost every forum I could find about the issue and have yet to find a solution.

1994 Lexus Sc300 2JZ GE

The Problem:
This issue started as the air blowing only when the car was in park and as soon as the shifter was pressed the air would cut off and the icons on the climate control would disappear. A month later it wouldn’t turn on at all, no icons no air only backlit. Occasionally the icons pop up for half a second then go away. The clock in the dash is dim and not adjustable.
I replaced all the fuses (besides the relays) in the interior and engine compartment fuse boxes. Every forum was paying extra special attention to the #11 fuse, which wasn’t even blown or corroded when I changed all of them (none of them were). It’s also important to note that my cigarette lighter works (and no there is not a coin in it)
Next I changed the battery (which tested bad) and the climate control unit. Both of which ended in the same results. The AC and heater were working perfectly fine until about 4 months ago.

in summary my climate control unit only lights up with no icons, my dash clock doesn’t adjust, and no air is blowing through the vents. None of the climate control buttons work. I’ve replaced all fuses, the battery, and the control unit.

Could it be a relay? If so where? Any other ideas?

Thanks!

 

Hello and welcome, Nickcab.

I'm not sure exactly what your main issue is here but you said you changed out the climate control unit to another one? From what model year was your replacement climate control unit? Lexus revised them a couple of times and they are only compatible between certain model years even though they should plug in the same way for all model years. The climate controller LCD screens can be replaced and that tends to be a common issue at least once in the life of an SC300/400 but you didn't mention that being a problem.

Are you sure that your A/C blower fan is in good working order? Also on 92-94 SC's there is an additional blower fan resistor that can in some cases go bad (though this tends to be rare).

And it doesn't seem related but I assume that your A/C magnetic clutch is coming on the way it is supposed to when you request the A/C to turn on?

Though rare it is possible that an SC300/400 main engine ECU with faulty capacitors can also cause some issues with A/C functions. For this we recommend sending in your ECU for new capacitor service to revitalize it back to normal operating condition. With that issue you would also notice drivability issues, running rich, rough running and/or starting issues if the main ECU capacitors need replacement. Generally Tanin Auto Electronix is recommended for this service by special request. Since you are located in California they have a repair office in San Diego I believe in addition to their main repair office in Wisconsin.

Main ECU capacitor issues manifest a little differently in each SC300 or SC400 even though there are some common signs. With the age of most SC's today it is a very common thing for many of them to need the ECU's old capacitors replaced with brand new ones of the same exact value from the same OEM supplier that Lexus originally manufactured them with. Alternatively all the required capacitor values from the correct brands can be bought from Digi-Key or Mouser Electronics but for most owners doing it yourself is only recommended for anyone with experience desoldering, soldering and restoring electronics circuit boards.

I know it sounds odd to suggest doing something about the health of the main engine ECU in order to restore A/C function but it apparently can be a factor in some cases with these cars.

The clock having an issue with operating can be repaired and would be part of an instrument cluster related service. Tanin Auto also does those repairs (as well as SC300/400 climate control LCD replacement if your display were burned out).

First before doing any of the above things:

See if you can get your climate control display to show any error codes. Read the following thread and follow the instructions in the first post which shows you how to activate the HVAC/climate-control diagnostic mode for code retrieval:

https://www.clublexus.com/forums/per...eed-codes.html

 

I tried to do the diagnosis on the climate control unit but nothing popped up. It could possibly be a burnt out blower fan and/or resistor; but does that explain why there are no icons on the LCD screen (or why the buttons don't work)? The "new" climate control unit is from a 93' and has new bulbs and a new LCD. Occasionally when I go to turn on the car or shift into park the climate controls icons will appear for a split second. My instrument cluster is fine, the reason I mention the dim un-adjustable clock is because on other threads and forums it was mentioned that the climate control unit, the instrument cluster clock, and the cigarette lighter share a fuse (which has been replaced even though the original was not corroded).

The problem is similar to the one discussed here:
(Referencing point 1) https://us.lexusownersclub.com/forum...ater-no-power/
https://www.clublexus.com/forums/per...t-working.html

 

Touching the brake and shifting from park establishes a ground drain into the system. It also draws more current due to brake lights. Check the grounds at the battery first then work your way back through the ones near the radio.

 

Obviously it's been a couple of years & this is a long shot. I am having the exact same issue in my 94 Soarer. I'm not new to these cars as I've owned a '95 SC300 for 17 years & I owned a '97 SC400 for a while during this time. This is the 1st time I've encountered this issue. Did you ever find a resolution to the problem? Problem, a/c is fully functional in park, press shifter button to change gears, loss of a/c functions. Put the car back into park & regain full a/c functions.