I have no heat!

[Britt89]

I have an 03 celica gt, and the heat wont come on all the time. it will come on if i get on it really good after the motor is at operating temp, and sometimes it will randomly come on but only after about 20 minutes of driving. i found out that these cars dont have a heater control valve, so im stuck as to what the problem is. once the heat comes on, its very hot but it just takes a bit of encouragement for it to come on.

i found a solenoid valve that has a huge vac line that is attached to the throttle body and then goes into the cabin, which i believe is for the vacuum operated heater/ air blender in the car, and theres a schrader valve in the line that goes to the cabin, so i ran the car on heat and cool and there was no vacuum in that line at the schrader valve, could that solenoid be bad? or what could it be? thanks for the help!

[bbmx952]

Ok, Im a little confused, are you saying that the heat does come on after the engine is at operating temp? Or is it that it sometimes comes on and sometimes doesn't when its at operating temp?

[Britt89]

it will come on way after the car is at operating temp. sometimes it will randomly come on, and sometimes i have to get on it really good. im thinking that the vacuum solenoid for the air blender is sticking. im going to hook up a vac pump to it tomorrow to see if the line going to the cabin will hold vacuum and if the solenoid is getting vacuum. but idk if thats even for the heat or not. its right behind the air box with a line going to the tb and one going down past the firewall. but we'll see.

[toyomoho]

The heater must have some kind of valve to control heat. Either by controlling the coolant to the heater or bypassing the hot air from the heater core (not likely).

The vacuum lines may supply vacuum to operate the heater control valve. Not sure about the Schrader valve. Some cars run a temp-sensing bulb into the climate control vent. This bulb helps control heater temp by opening and closing the coolant valve.

Suggest you follow the coolant lines to the heater core and see what you find. There should be a valve somewhere to control the coolant flow. Guessing you will need to go under the dash to find this valve.

[Britt89]

Originally Posted by toyomoho

The heater must have some kind of valve to control heat. Either by controlling the coolant to the heater or bypassing the hot air from the heater core (not likely).

The vacuum lines may supply vacuum to operate the heater control valve. Not sure about the Schrader valve. Some cars run a temp-sensing bulb into the climate control vent. This bulb helps control heater temp by opening and closing the coolant valve.

Suggest you follow the coolant lines to the heater core and see what you find. There should be a valve somewhere to control the coolant flow. Guessing you will need to go under the dash to find this valve.

well normally, the heater control valve is in the engine bay close to the firewall. there isnt one anywhere on this car, and the dealer said that there is no heater control valve. so the only other way to control the heat is with the blender, which i believe is vacuum operated.