AC blows hot sometimes

[pinchshopper]

We have a 2002 SR5 that we bought last fall. Sometimes the AC will start blowing hot air. If you turn the temperature control dial to hot and then back to cold, you can hear a change in the airflow and it starts blowing cold again.

Anybody ever had this happen, or know what's going on ?

 

[Richard808]

I have not had this problem but if i may ask does the air stay hot if you dont cycle the temp dial or will it eventually start blowing cold after some time passes? im not too familiar with the 4runner ducting but i believe its cable operated and the cable moves a hot/cold air flap that will allow either all cold or all hot or let in a mix of both. think of it as a shower that has only one lever to control both hot and cold water. ive seen some electric operated ones where the motor is too weak to move the flap and the flap is usually spring loaded to be on hot air unless the motor moves it. so it will want to go to hot air by default if that makes sense. you may have a messed up cable or something but again thats just a total guess as ive never actually seen this system. hope this info can offer some kind of help.
If you can see where the cable leads to or see the motor if its electrically operated you should be able to tell if it full open to cold air or not by looking at it while its working and then looking again when it fails. possibly even be.able to tell by cycling it while watching it but i dont know what youd have to remove to get to it. most cars its behind the center of the dash toward the bottom.you may need to see a manual as to where it is.

 

[pinchshopper]

I have not had this problem but if i may ask does the air stay hot if you dont cycle the temp dial or will it eventually start blowing cold after some time passes? im not too familiar with the 4runner ducting but i believe its cable operated and the cable moves a hot/cold air flap that will allow either all cold or all hot or let in a mix of both. think of it as a shower that has only one lever to control both hot and cold water. ive seen some electric operated ones where the motor is too weak to move the flap and the flap is usually spring loaded to be on hot air unless the motor moves it. so it will want to go to hot air by default if that makes sense. you may have a messed up cable or something but again thats just a total guess as ive never actually seen this system. hope this info can offer some kind of help.

I think it would continue to blow hot if I didn't cycle the temperature control knob. This weekend I had to cycle the knob 5 or 6 times to get it to change. Usually, you only have to do it once. I checked the actuator under the hood, and it responds when I cycle the temperature knob, but for some reason it changes on it's own sometimes.

 

[Richard808]

sounds electrically operated. what kind of actuator is it? if theres a electrical connector try unplugging it while its cold if it goes hot then its set to hot by default and will only go cold when the actuator is energized. the actuator could be getting weak like a starter solenoid it gets stuck and clicks alot until it eventually frees up and moves. motors also can act that way and get weak and have a hard time initially but once it moves some it will work. i am thinking the actuator is bad.

 

[LittleCaesar]

Possibly your AC amplifier is going bad. It is located right under the glove box, mounted onto the lower case unit. My friend's 2001 AC amplifier (for his Auto AC, they call it a magnetic clutch relay) went south on him two years ago. He would be driving when the AC was cold, then hot, then cold, then stayed hot. His indy shop mechanic changed it and he has been good to go to this day.

The manual will actually give pics.
Toyota Tacoma/ 4Runner/ Tundra/ FJ Cruiser Factory Service Manual Page

 

[pinchshopper]

sounds electrically operated. what kind of actuator is it? if theres a electrical connector try unplugging it while its cold if it goes hot then its set to hot by default and will only go cold when the actuator is energized. the actuator could be getting weak like a starter solenoid it gets stuck and clicks alot until it eventually frees up and moves. motors also can act that way and get weak and have a hard time initially but once it moves some it will work. i am thinking the actuator is bad.

The actuator moves the cable that switches from hot to cold. It is not binding. When I tested it, it moved from one extreme to the other when I adjusted the knob. Something is sending a different voltage to the actuator and making it change by itself from cold to hot.

 

[pinchshopper]

Possibly your AC amplifier is going bad. It is located right under the glove box, mounted onto the lower case unit. My friend's 2001 AC amplifier (for his Auto AC, they call it a magnetic clutch relay) went south on him two years ago. He would be driving when the AC was cold, then hot, then cold, then stayed hot. His indy shop mechanic changed it and he has been good to go to this day.

The manual will actually give pics.
Toyota Tacoma/ 4Runner/ Tundra/ FJ Cruiser Factory Service Manual Page

I vaguely remember replacing one of those years ago on a vehicle, but I think it was for a friend. I can't for the life of me remember what kind of problem they were having. I think it had something to do with blower power or speed. Is this part tied to the temp control circuit?

This problem seems to occur shortly after starting the vehicle or within a few miles of leaving the house. Although, I have noticed that the foot air sometimes seems to blow a little warmer, while the upper vents are still blowing ice cold.

 

[LittleCaesar]

Next time it does it, and once you know where the amplifier is located, give it a good rap with the hand and see if it turns back on. I think the resistor or diode goes bad on it, at least that is what the AC technician told my friend.