Heat Loss inside cabin

[modmonster2008]

Hey guys, I noticed this morning that my heat stopped working. So before anyone makes any assumptions or anything, I do have coolant in the system, it was working perfectly yesterday, and the two heater hoses both inlet and outlet are around the same temperature based on my laser temp reader. I did notice that the heater valve was shut even with the climate control on 85 so i bypassed the VSV and directed the vacuum to the valve itself so it stays open, but there is still no heat at all. I do notice as well that even when i move the climate control from 65-85 i absolutely do NOT hear the blend door moving within the dash like i used to. Is there any ways of me checking for any faulty components or anything to start with? I dont want to take the whole dash off just yet, let me know guys, thanks!

 

[IJ.]

I had the AC Amplifier fail on my car way back...

Blue Box over the glovebox, also had the Temp rheostat fail another time which caused simular symptoms.

 

[modmonster2008]

IJ where is the temp rheostat located? ill do some checks on those, would this cause the previous issue of heat at 85 but when the CC is at 65-84 its just blowing cold?

 

[IJ.]

In early cars it's a slider and in late I believe it's a rotary, the control you use to raise/lower the temp.

 

[jetjock]

Couple of things if I may Ian. First, in USDM cars the climate control system is all push button. Second, the AC Amplifier exerts control only over the compressor. The System Amplifier, located within the climate control head (what Toyota calls the AC Control Panel) controls the Air Mix servo.

 

[IJ.]

Couple of things if I may Ian. First, in USDM cars the climate control system is all push button. Second, the AC Amplifier exerts control only over the compressor. The System Amplifier, located within the climate control head (what Toyota calls the AC Control Panel) controls the Air Mix servo.

By all means do

Maybe when I replaced my rheo panel it was the amplifier that fixed my issues the second time, 1st time all I changed was the blue box and that sorted the issue but it may have been something under the dash I moved/reconnected that "fixed" it and nothing to do with the AC amp!

 

[jetjock]

Yeah, could have been something loose. His problem is typical of a certain kind of failure though, one which is pointed out in the manual.

 

[modmonster2008]

Which manual would that be in?

 

[3p141592654]

This one

http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=AC&P=1

 

[modmonster2008]

Did the servo motor test per TSRM it is functioning just fine. NOW i have a question, the Climate Control is set to 85, but i hear the servo motor making short moving noises and the temp changes accordingly to the motors movement, what could be the cause of the motor to be moving back and forth like that intermittently?

 

[jetjock]

The integral feedback pot is worn causing the system to chatter in open loop. Good luck with that. The servo is around $500 and may not even be available. Plus the job requires dash removal.

 

[modmonster2008]

so you are saying in general that my servo motor is bad? or is something else giving it that bad input making it move around?

 

[7M4EVR]

The integral feedback pot is worn causing the system to chatter in open loop. Good luck with that. The servo is around $500 and may not even be available. Plus the job requires dash removal.

Yikes...this is where in Nebraska folks would either carry some blankets or rig up a power adapter and a small space heater lol

 

[3p141592654]

The servo position sensor is bad, which is not a user serviceable part in Toyota's eyes. Getting to it is non-trivial, a new one is expensive (or maybe discontinued) and putting a used one in is rolling the dice given the pain of replacing it twice!

I haven't seen anyone try to repair it, but if it was me I would get a used one and see if it could be disassembled and repaired. This problem is also cropping up on electronic throttle modules, and there are places out there that have figured out how to replace the position sensors in those things, so there is no fundamental reason why this one couldn't also be replaced with some investment of time and materials. Is it worth it to try? Not for me to answer.