80-Series Climate Control Question...

[kolkim82]

First off, this is my first attempt at posting on one of these forums so I'm sure I'm doing something wrong but I'm at a loss and don't know what else to try.
I've got a 1997 Lexus LX450. I purchased it in Sept. and can't get it to blow hot air. First, the blower only works on hi so I have replaced the blower motor and have a resistor and amplifier ordered to hopefully fix that. But my main issue is the temp of the air it blows. I have the temp set to 80 degrees and I only get moderately warm air no matter where I have the air directed (floor, defroster, etc.). I checked all the heater hoses and they are all hot on both sides of each heater core, so I don't believe I've got a heater core blockage. The heater valve is working. I took the climate control unit out and moved the little switch on the back of the unit from Auto to Manual. It still only blows cold / moderately warm air. I then thought maybe I've got air in the system. So I elevated the front end a couple feet higher than the rear, removed the radiator cap and let the vehicle idle in hopes that any air would eventually escape. After two hours idling with the front end elevated I finally got nice HOT air! So, I thought I had it fixed. The next day, I put the front end back on the ground, put the radiator cap back on and cranked it up. Again, I only got cold / moderately warm air. This after idling for over an hour, so I know the engine was hot. Now I'm at a loss... Could the cabin air temp sensor be malfunctioning to make the system think it doesn't need to blow hot air? If so, wouldn't switching from Auto to Manual have eliminated this? I'm just puzzled because I got it to blow hot air once but never again. Any of you guys got any ideas?

 

[HungryJ0e]

Sounds like you're well on your way to diagnosing the problem.

To take the cabin air temp/climate controller out of the equation, I recommend disconnecting the heater valve control lever arm from the control valve in the engine bay, and manually place the heater valve all the way open. If you get hot air through the vents, you know that that side of the system is working and you have a control issue. If you don't get hot air, you've only got a few other areas to look into.

Assuming you get hot air from the vents, next step is to reconnect the heater valve control lever to the valve, and observe its operation when you call for heat. Sometimes the lever arm is misadjusted, and it won't fully operate the valve... typically it won't *shut* the valve all the way but it's certainly possible to have the opposite problem where it won't open the valve... it's a fairly simple procedure to undue the lock nut and adjust the lever arm for full action.

If the lever arm isn't moving at all, or is moving erratically, you've got an issue with the climate control system itself...

 

[RiverCityDave]

Sounds like you're well on your way to diagnosing the problem.

To take the cabin air temp/climate controller out of the equation, I recommend disconnecting the heater valve control lever arm from the control valve in the engine bay, and manually place the heater valve all the way open. If you get hot air through the vents, you know that that side of the system is working and you have a control issue. If you don't get hot air, you've only got a few other areas to look into.

Assuming you get hot air from the vents, next step is to reconnect the heater valve control lever to the valve, and observe its operation when you call for heat. Sometimes the lever arm is misadjusted, and it won't fully operate the valve... typically it won't *shut* the valve all the way but it's certainly possible to have the opposite problem where it won't open the valve... it's a fairly simple procedure to undue the lock nut and adjust the lever arm for full action.

If the lever arm isn't moving at all, or is moving erratically, you've got an issue with the climate control system itself...

This is your next step.

 

[joxeale]

My cruiser has always had this issue since I bought it 4 years ago, only coldish air, never warm/hot air. I replaced most main parts on the AC system back when I got it, compressor, condenser, evap and others. Still same thing. Only recently, I noticed the damn Vent Control Motor Servo was stuck since it started making noise when I put it into cold air, so my guess is that it is in fact stuck right in the middle to where the cold air is never that cold or the warm air is never super warm. Anyways, thought I mentioned it since I see you haven't checked on that yet. I ordered a used unit on ebay, once I replace it I'll update my results here (if I remember lol). Good luck

 

[Timpanogos Slim]

blower only running on high is more likely a problem with a burnt up connector in the relay pack that selects the fan speed by selecting resistors. it's sort of on top of the blower housing but toward the firewall. I had to replace a terminal on the connector.

 

[greentruck]

...I then thought maybe I've got air in the system. So I elevated the front end a couple feet higher than the rear, removed the radiator cap and let the vehicle idle in hopes that any air would eventually escape. After two hours idling with the front end elevated I finally got nice HOT air! So, I thought I had it fixed. The next day, I put the front end back on the ground, put the radiator cap back on and cranked it up. Again, I only got cold / moderately warm air.

Just a thought. Sounds like air in the system is at least part of the problem. You should top it off and put the cap back on the radiator while the nose is still up in the air. Might be worth giving that procedure another try.

 

[Mrtwooooo]

My guess is the blend door is not moving to allow air to flow through the heater core. Behind the dash there is the "box" that holds the heater core and all of the flaps to direct air. As you move the temp slider from cold to hot a motor turns a flap to let more air flow through the heater core instead of bypassing it (this is my loose understanding). My guess is maybe the black box in the photo is what is controlling that. There are also a few threads regarding the blend door that may help you further.

 

[Ronald Rooij]

I have a question that more or less relates to this issue (LX450, 1997).

Sometimes, when I start the car, the ventilation and heating control panel does not come on. No lights no fan, nothing. Suddenly after maybe 5 minutes the control panel comes on and everything works ok.

I had a similar problem with the direction indicators. First they do come on but don't blink, and after maybe 5 minutes they start blinking.
I assumed the problem might be related with a lower voltage on the battery after start-up, which could affect the relay. I changed the (25+ year old) relay and the problem was solved.

I did the same with the relay on the control panel. No effect. The control panel is ok, I recently swapped the older leds for new brighter ones and tested it on the bench.

Are there more relays or other items that are affecting the control panel?

 

[RivMan]

I have a question that more or less relates to this issue (LX450, 1997).

Sometimes, when I start the car, the ventilation and heating control panel does not come on. No lights no fan, nothing. Suddenly after maybe 5 minutes the control panel comes on and everything works ok.

I had a similar problem with the direction indicators. First they do come on but don't blink, and after maybe 5 minutes they start blinking.
I assumed the problem might be related with a lower voltage on the battery after start-up, which could affect the relay. I changed the (25+ year old) relay and the problem was solved.

I did the same with the relay on the control panel. No effect. The control panel is ok, I recently swapped the older leds for new brighter ones and tested it on the bench.

Are there more relays or other items that are affecting the control panel?

I had a similar issue with my 97. There's a module under the dash that collects water from a windshield leak. Mine had about a half inch of standing water, and had corroded the circuit board slightly.

Looks like this and is mounted next to the brake pedal under the dash. I'd open it up and see if that's the issue.

-Rob

 

[surfpig]

I had a similar issue with my 97. There's a module under the dash that collects water from a windshield leak. Mine had about a half inch of standing water, and had corroded the circuit board slightly.

Looks like this and is mounted next to the brake pedal under the dash. I'd open it up and see if that's the issue.

View attachment 3643296

-Rob

I had the same problem with mine. I cleaned up all the corrosion, hooked it back up and it worked. Till it filled back up with water!

I re-cleaned it, then I reinstalled it upside down and it's been fine ever since (replacing the windshield also helped).

OP: there's a little air intake sensor on that control panel, with a little tube that's supposed to be attached to it. Might be something to check.

 

[Dark Knight]

Similar issue when I purchased mine. Turned out the cable from servo to the heater valve on the firewall was crimped and not moving properly. Replaced the cable and it’s working perfectly.