97 Es 300 'gremlin-In-The-Heat/a/c Fan Unit'

[mbh]

My Heat/ AC dash-board-unit is all soft-touch, push button controlled.

My Heat / AC fan will come on full blast, at the most random time of day, and under any/all drive and weather conditions.

Then...i cannot lower the fan setting (to say 1/4 to 1/2 blast).

Then....I can't turn in off, unless I hold my finger down on the 'OFF' button, and wedge a 'credit card' in to hold it in the 'off' depressed position.

I can 'reset' things when I turn off car and remove my credit card. But then....who knows when it will come on again.

I've had to warn my passenger, because it can scare you at first!

Help!

[lexis lexus]

your hvac system is controlled by computer, not sure if it's the main ecm or if there is a computer built into the dash control module.

there is a way to access diagnostics on that system, but it'll be in the factory service manual, not in a haynes. if you can find it, it's pretty easy (at least on my '94) and the diagnostic run will tell you what parts of the system aren't working, could be a relay, could be the dash control unit, could be any one of a dozen components the system that the diagnostic checks

might want to take it in to toyota or lexus but then it'll be expensive.

another option is to pull a heat/ac dash control out of a wrecker yard (on the assumption that that's what's malfunctioning) and replace the one you have.

Let us know the outcome.

LL

[mbh]

What is a heat / ac dash control unit?

[mbh]

I went to a junk yard and purchased a new electronic air/ heating control unit (from a 2000 ES 300). Installed into my 1997 Lexus ES 300. Plugs were perfectly compatible (although I did not check exact pin color and position wiring). The fan and motor settings work great, but the air conditioning and heating will not work, when I force either to come on.

I assume the wiring is different? but I cannot find a wiring diagram to compare my 1997 to the 2000 wiring.

Any ideas?