No Heat! Help!!!

[rob3529]

1998 Toyota Avalon with auto heat/ac. My heat will not stay on. If I switch from off to Auto the blower will give a quick blast but that's it. I used to be able to press all of the fan speed buttons over and over and eventually the fan would stay blowing. Now that doesn't work. All of the controls light up and appear to function, but they don't. any suggestions?

[Jigg007]

You said it does a "burst" when you press auto. do you get that same burst when you push the HI button? It sounds like the control panel might be at fault. but you might want to check out voltage at the blower motor.

Also, does the panel function? In my 96 if I push the auto button and cycle the thermostat dial around it will change fan speed and duct selection. Does your show this operation based from the indicator lights? If it doesn't, that may hint at a faulty panel.

Again, I'd check the voltage at the motor to be sure. Most cars I've worked on use blower resistors, but with servo controls in the duct routing, I wouldn't be surprised if the Avalon used PWM for motor control. (which rules out the cheap fix!)

[rob3529]

Thank you for your response. I was mistaken about the burst from Auto to Hi. The burst happens when I switch from Off to HI, and it doesn't always work. All of the vent position buttons work, I can hear the servos moving. The temperature adjustment dial does nothing in terms of making the blower come on. I don't know what PWM means or why that would rule out the cheap fix. Is the cheap fix the resistor?

[Jigg007]

The "cheap fix" is the blower resistor, which most of the time is the reason for a failed motor. However, the climate control system does not use a blower resistor, and instead uses a fancy module that controls the fan speed. I dont know if your system ever worked, but you would notice it when AUTO mode kicks in and how the fan speeds up smoothly, as opposed to a 1, 2, 3 and 4 speed setting. This is done by PWM, a method that is more functional and efficient than using a set of resistors to select motor speed, but alas more expensive.

That said, the easiest way to start diagnosing is you have to measure the voltage at the blower fan under/behind the passenger glovebox. If you have voltage present when a fan speed set to max, then your blower motor is bad. around 50 bux for a new motor. If there is no voltage present at the motor, it could be a whole plethora of things. The fact that the control panel lights up most likely rules it out, leaving culprits being the AC amplifier, Motor controller, Motor, or a bad connection. Best start checking out the motor.

[comwiz]

Did you fix this? You should not check only the resistor but also capacitor of the blowing motor. The capacitor keeps your blowing motor on.