Max Cool Blows Hot Air

[no3puttin]

My wife's 2001 RX300 (55,000 miles) recently began blowing HOT air out the vents when the thermostat is lowered. Is there a "Main" air controller or vent valve or ??? that switches the air feed to the vents. All vents appear to to be operating properly depending on control panel settings, but no cool/cold air comes out no matter where the temperature control is set. The harder it tries to cool, the more HOT air it blows, the higher the temperature goes, the harder it tries to cool, etc...

Any help would be appreciated...TIA

Russ

[wwest]

My wife's 2001 RX300 (55,000 miles) recently began blowing HOT air out the vents when the thermostat is lowered. Is there a "Main" air controller or vent valve or ??? that switches the air feed to the vents. All vents appear to to be operating properly depending on control panel settings, but no cool/cold air comes out no matter where the temperature control is set. The harder it tries to cool, the more HOT air it blows, the higher the temperature goes, the harder it tries to cool, etc...

Any help would be appreciated...TIA

Russ

First, if you put in max hot all the sensors are bypassed and the reheat/remix door is "blindly" driven to the full remix, max heat position. The opposite is true in max cool position.

If that doesn't work then I would disconnect the battery for 10-15 minutes. When you reconnect the battery you should hear a bit of "buzzing" and "wherring" behind the dash as the HVAC ECU recalibrates all of the servomotors.

The see if it work properly.

[no3puttin]

wwest,

Thanks for the reply...

I disconnected the battery for about an hour, but did not listen for servo calibration. The problem is still the same.

With the controls set at Max Cold or Max Heat, the fan only blows HOT air...

Any other suggestions??

Where can I find diagrams etc. for the heating/cooling system?

Thanks

Russ

[wwest]

wwest,

Thanks for the reply...

I disconnected the battery for about an hour, but did not listen for servo calibration. The problem is still the same.

With the controls set at Max Cold or Max Heat, the fan only blows HOT air...

Any other suggestions??

Where can I find diagrams etc. for the heating/cooling system?

Thanks

Russ

Techinfo.toyota.com but with a membership fee, minimum of 1 day.

[lenore]

Read post 19 by dcfish :

http://us.lexusownersclub.com/forums/index...otors&st=15

[no3puttin]

Thanks lenore...I'll try to follow the procedure in the link this morning.

I'm not sure the servo is the problem since the system seems to adjust the venting properly (heat on floor, cool on dash, defrost good, etc.). Does one of the servos control heat vs cool? It's just that no matter where the thermostat (hot/Cold) the system vents properly but ONLY blows HOT air.

Thanks for your help.

Russ

[lenore]

I believe there are three servos.

[no3puttin]

Thanks...

I didn't get to look at it today afterall, so now it'll be sometime next week.

I'll post the results.

Russ

[no3puttin]

lenore, anybody??

2001 RX 300 heating and a/c system only blows HOT air. I removed the glove box and watched the air servos redirect the air properly, but it only blows hot air (temp setting only affects the air distribution and not the air temperature). Is there a main air vent/valve that could cause this?

TIA

Russ

[wwest]

lenore, anybody??

2001 RX 300 heating and a/c system only blows HOT air. I removed the glove box and watched the air servos redirect the air properly, but it only blows hot air (temp setting only affects the air distribution and not the air temperature). Is there a main air vent/valve that could cause this?

TIA

Russ

The air mix reheat/remix vane/door/film is inside the plenum area in the center of the dash. The servomotor "doors"/vanes you see through the filter opening is only the fresh/recirculate functionality.

What happens before the engine coolant heats up?

All, ALL, system airflow first passes through the A/C evaporator and is cooled if the air condition section is operational. After passing through the A/C evaporator a selected portion (max heat = ALL) of the airflow is diverted to flow through the heater core. Downstream of the heater core the two air masses are remixed to provide you with the proper temperature airflow into the cabin.

[no3puttin]

thanks lenore...

This morning I discovered that if the thermostat is set low enough (below cabin temp) when first started it operates properly and blows cold air. I believe the a/c was even cycling. When I raise the thermostat (above cabin temp) and go to heat everything works correctly, hot air from dash to dash/floor to floor if temp differential is sufficient. However, when I lower the thermostat to below cabin temp again, only hot air comes out (even though the venting operates correctly, ie. foor to floor/dash to dash).

If I turn the system OFF, I hear what sounds like some sort of flap fall, turning the system back on usually works fine until you need heat and the cycle starts over again.

Oh, one thing that has happened since we got the vehicle (2yrs ago) is the a/c panel light comes on whenever you go to AUTO mode, regardless of the thermostat setting or the temperature. It has never been a problem, so I assumed it was normal.

I'm hoping to continue troubleshooting this problem with help from the forums.

Thanks again...

Russ

[ChrisDay]

thanks lenore...

This morning I discovered that if the thermostat is set low enough (below cabin temp) when first started it operates properly and blows cold air. I believe the a/c was even cycling. When I raise the thermostat (above cabin temp) and go to heat everything works correctly, hot air from dash to dash/floor to floor if temp differential is sufficient. However, when I lower the thermostat to below cabin temp again, only hot air comes out (even though the venting operates correctly, ie. foor to floor/dash to dash).

If I turn the system OFF, I hear what sounds like some sort of flap fall, turning the system back on usually works fine until you need heat and the cycle starts over again.

Oh, one thing that has happened since we got the vehicle (2yrs ago) is the a/c panel light comes on whenever you go to AUTO mode, regardless of the thermostat setting or the temperature. It has never been a problem, so I assumed it was normal.

I'm hoping to continue troubleshooting this problem with help from the forums.

Thanks again...

Russ

Hi Russ

I'm have a very similar problem with my 2001 RX300 (65k). All the controls seem to work correctly to speed up and slow down the fan as I change the temp setting. When its at ambient temp the fan is basically off. BUT there is nothing but super hot air coming out all the time. I did the diagnostic for the ac/heat system and got 00 for codes = all ok. I suspect the air diverter that mixes the hot/cool air is physically broken (so the servos look like they are working but not moving anything inside) and the hot air just overwhelms anything the AC is putting out. Not sure when I can get to it but the car not really drivable in the summer. I'll repost here if I have anything to report.

Best of luck to you.

Chris

[ChrisDay]

Well I somehow got motivated - maybe cuse its 95 degrees and Im sick of no air.

I took the glovebox out and found the shaft for the air mix servo was broken off.

I doubt I can fix it so I'm going to have to fess up the 160.

Hope you fair better.

[Sugar Sugar]

Same thing is happening to me it blows hot air no matter what , so it was the servo motor ? 

[Sugar Sugar]

The heat works fine then fmip it to AC and it bliws nouthing but hot air and turn it all off and hot air still comes out ...is it the servo motor?