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Where is the evaporator temperature sensor?

Discussion in 'Generation 1 Prius Discussion' started by ronlewis, Feb 15, 2024.

  1. ronlewis

    ronlewis Active Member

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    I'm getting a 13 code on my AC for the evaporator temperature sensor, according to this service manual I have, but then it's not included in any of the component location pics. The best I can deduce is that it's what a pic calls the "thermistor." There's a pic of a test of the "evap temp sensor" being tested by immersion in cold water and it looks like the part with the thermistor name in the pic.

    But, that doesn't help. Unlike most of the other components in the pic that have lines showing where they attach to the car or other parts, that pic doesn't connect the thermistor to anything. It's just sitting by itself off to one side.

    Better question: is there any other reason for a code 13, before I go to the trouble of water-testing this? The manual says to replace the AC amplifier for a 13 if the sensor is good, or the harness in between. This car operates fine otherwise (not the car with electrical probems).

    With the engine running, the compressor clutch doesn't lock when I turn on the AC, and there's not 12v at the compressor connector with key ON, but I can provide 12v to the connector and the clutch clicks/moves as it should. I've swapped all the AC relays with those of a known-good car and both cars didn't change, so I'm assuming the relays are all good.

    Figured I just need refrigerant, and the pressure switch was cutting the compressor out. but I'm not confident that my manifold gauges seal properly. Would the compressor not kicking in cause the evap sensor to set the 13 code? IDK where that sensor is, but if I have to remove the evaporator, I bet it's a PITA.
     
  2. ChapmanF

    ChapmanF Senior Member

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    Pretty sure it's stuck in between a couple of the evaporator fins.
     
  3. Tombukt2

    Tombukt2 Senior Member

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    Yeah it'll be wedged in some thins coming out of the evaporator case I've never changed one but I've changed a bunch of other stuff in similar type of Toyota cars so when you try to turn on the air conditioner properly with the relays in place Do you feel any of the relays clicking or making connection when you push your air conditioning button or whatever it is in your car that you do And some of my older cars I push a blue button it lights up I hear the clutch activate The clutch has 12 volts going to it it locks up spends the compressor starts to make cold and that's that your compressor's not locking up from the get-go but it works because you can apply voltage to it so when you push the switch or the knob or what have you why are you not getting 12 volts to the clutch wire seems to me it would be a body control module air conditioning amplifier that sort of thing probably not the sensor.
     
  4. ronlewis

    ronlewis Active Member

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    Thanks, guys. That doesn't sound good. Getting to the evaporator, from what I can tell, is a major project - refrigerant, coolant, AC unit, blower unit, special hoses in tight places. The manual says there are three possible causes - the sensor, the harness and the AC amp - and checking voltages on the sensor connector tells you which. So, does anyone know it I can access that connector without removing/draining/discharging/etc.? 2 out of 3 solutions don't require replacing that sensor.

    Still, does that seem odd, that sensor going bad? Like I asked above - could this code be setting bc it assumes there's refrigerant, or that the compressor isn't turning, etc.? In other words, can the events that trigger the sensor code be the result of other events that, if repaired, will make this code go away? It seems possible if for no other reason there's nothing, possibly, in the evaporator to sense. Maybe be turning the AC on after it sat in the auction for some time and lost it's refrig, is what triggered the evap sensor code.

    Yeah, I'm trying to rationalize some way to not pull the AC and blower unit. But, if that's what has to be done, at least I may not have an refrig to collect, and I might be opening those fittings anyway looking for the leak.
     
  5. Tombukt2

    Tombukt2 Senior Member

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    You should be able to get to the sensor wires as it penetrates the evaporator case. Just check the schematic for the wire colors I guess they have to penetrate the case to go to wherever the AC amplifier is used to be slid in a little plastic box in my other cars I don't know where it is in this car or even in my generation two or three's I'm sure some computer controls it. And I would guess if the air conditioner isn't running the temperature sensors not going to sense any temperature right? So I guess it could send a not cold signal to something that's interested.
     
  6. ronlewis

    ronlewis Active Member

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    Thanks, Tom. OK, I confirmed that what the service manual calls the evaporator temperature sensor is what the wiring manual calls the AC thermistor. Still can't tell where the connector is. Here's pics. One shows the dash locations of many components - the thermistor is A12. It's line points to what looks like a spot right next to the AC amplifier by the AC controls in the dash.

    However, there's no matching connector on the amp. All the pics show the thermistor with it's own 2-wire (loop) connector, but the wiring diagram and a pic of the amp terminal pin outs (not incl) don't show a spot for a separate 2-wire connector going into the amp, even though the illustration shows the connector right by the amp.

    Good news, this is the car that I replaced the dash bezel in last month - broke it trying, but am still using it. So, it comes off easy. My hope is that I've simply not plugged in that connector putting it back together.
    therm-insp hosted at ImgBB — ImgBB
    therm-dia hosted at ImgBB — ImgBB
    thermistor-loc hosted at ImgBB — ImgBB
    ac-unit hosted at ImgBB — ImgBB
     
  7. ChapmanF

    ChapmanF Senior Member

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    The diagrams can show just the portions of a connector that are relevant to a particular circuit, so sometimes you can take them too literally. For example, the second image you linked shows the thermistor connections to be pins 1 and 2 of connector A9 at the amplifier. But when you flip to section K in the wiring diagram, you see that A9 is a 22-pin connector. You are looking for pins 1 and 2 of that, not of some mythical 2-pin connector.

    In a way it's unlucky that the thermistor just happens to use pins 1 and 2 there. If the diagram had showed it using, say, pins 4 and 15, that wouldn't have fooled you into looking for a 2-pin connector.

    I see the instructions for access to the thermistor itself start with removing the blower unit. So the thermistor is on that side of the HVAC box, with the blower unit in the way.

    I remember Gen 1 had special provisions for removing the blower unit, should that ever be necessary, without full dash removal. Remove the glove box door and you can see the plastic brace that runs across the opening has two cut points molded into it, and two screw bosses just outside of those. You could cut through the brace at the marked points and be able to take out the blower unit that way. On reassembly, you would use a metal repair brace available as a dealer part, attaching it with screws into those provided bosses.

    It wouldn't surprise me, though, if by now the repair brace is no longer orderable.
     
  8. ronlewis

    ronlewis Active Member

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    Thanks for helpiing. I'm probably not communicating well. My confusion is that the pics of the thermistor show it with the two-wire connector. Here's the pic of the test page showing the connector and two test leads:

    thermtest hosted at ImgBB — ImgBB

    All the rest of what you describe is exactly why I'm confused. The wiring diagrams shows the sensor circuit beginning and ending in the amp terminal connector and doesn't show any two-pin connectors, splices, JBs or any such interruption to the circuit where the two-pin connector can join.

    If there's no two-pin, if the circuit is direct-wired to the amp, that'd be fine, but there'd be some different way, if any at all, to test the sensor.

    Do you have an opinion as to whether that DTC could be a secondary effect of some other issue - maybe something not producing whatever the sensor is supposed to sense?

    I do see those Blower Unit instructions, with the brace feature in the manual. It doesn't look too hard. Just don't want to go there if I don't have to.

    I still don't have refrig pressure readings that I trust. I believe there's none. An evap sensor wouldn't cause a loss of refrig, so if it's empty I definitely have another issue. I'm going to get the pressure checked today. I'm thinking that I can pump some refrig in to see if it kicks the compressor on, find the leak, and fill it up, whether the evap sensor is bad or not and won't lose the frig. But, if I had to remove the AC unit to get to the evap, then I'd have to evacuate the system again.

    Do you think a bad evap sensor circuit would stop the amp from powering the compressor to let me go that route?
     
  9. ChapmanF

    ChapmanF Senior Member

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    I don't see any instruction that you have to remove the A/C unit to get to the sensor ... just the blower unit that's in the way.

    As for the refrigerant pressure, Gen 1 doesn't have a pressure sensor, just a dual pressure switch, open if the pressure is too high or too low, closed if it's anything less wrong than that. Should be easy enough to check with a meter (there also should be a specific code if the switch is open).

    The two-pin connector attached to the evap sensor itself is A12, and looks like this:

    [​IMG]

    Both wires are white (how distinctive!) and the location diagram looks like you find it poking out near a low corner of the A/C unit by the passenger's feet.

    I wouldn't have thought an evap sensor would lock out compressor operation, but I guess I wouldn't rule it out either, as the amp then would be missing an input it wants for controlling the compressor.
     

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  10. ronlewis

    ronlewis Active Member

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    Thank you, sir. Everything on hold a few days now for a funeral.
     
  11. ronlewis

    ronlewis Active Member

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    OK, we may have answered that question - no refrig can lead to a code 13.

    The tech's gauges said my refrig was low. He put half a can in and the AC kicked right on. But, we could also hear it leaking out the condenser. This car had the slight front end wreck and it didn't look like the condenser/radiator got damaged to me, but apparently so. My parts cars have good condensers, so I'll swap one over. probably get a new dryer, etc. I assume I've lost all my oil too? I think these cars take different compressor oil than my other old cars. Pull a vacuum, and it should charge right up. We'll see if the code comes back.

    My father passed today so I won't be able to finish this until later next week. I'll get them swapped over the weekend, but not charged up before I leave. I'll update.
     
  12. ChapmanF

    ChapmanF Senior Member

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    I'm sorry for your loss.
     
  13. ronlewis

    ronlewis Active Member

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    Thank you, sir. He was 92 and had a good life. He died in peace.
     
  14. Tombukt2

    Tombukt2 Senior Member

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    Sorry for your loss big guy Do the best you can and have a good celebration of life You probably haven't lost all your oil just swap the condenser out it'll have some oil in it unless you're turning it over trying to run it out your compressor has some oil stored in it because it just does usually overtime people have too much oil in these things It won't hurt anything. And once you get that condenser swapped out vacuum it down and gas it up you should be good for years to go again sorry for this trying time and life dreams every two or three weeks I'm going to a funeral these days it's quite the thing.
     
  15. ronlewis

    ronlewis Active Member

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    Thx, Tom. Yep, my generation is falling like dominoes these days. And definitely more light from one end of my tunnel than the other. I'm just fighting through that hard time when you learn to accept it.
     
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  16. ronlewis

    ronlewis Active Member

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    Well, that didn't work out. I have so much going right now and don't have the energy to mess with this car. Plus, I wanted to help the son of a mobile tech I knew who passed away last year. The son took over his business.

    I don't trust my HF manifold gauges, and had got him to help me find the condenser leak in my AC. So, I pulled a known-good radiator/condenser assembly off my parts care, but I paid him to put it on this car and charge it up. I picked it up today and the AC seems to work fine, but I didn't get to test it much because there was a CEL on now. A p0115. I just live a mile from there, but before I could get it home, my temp light lit up. I slowed down to make the ICE stop and coasted home on battery. Before I got there, the temp light went back out, as I expected it too.

    So, that made me think it really was getting hot, and not just the coolant temp sensor issue that 0115 points at. I think the issue is that my tech didn't fill it all the way up with coolant. He only had to drain a little out to keep it from coming out the radiator hoses when disconnected, but that would still leave the radiator full. So, I provided him an entire radiator assembly, but it wasn't full of coolant. I think he added back in what he drained out, but didn't add enough to refill the swap radiator.

    No problem. We discussed it before I left, and I had a gallon of Toyota coolant at the house. All he had was green stuff.

    So, I think that solved that problem, but the inverter reservoir was low too, so I topped it up, but it was leaking out. Turns out it's cracked the back ear off, so bad that the reservoir is leaking. And the hose that carries that coolant attaches to the radiator fan shroud. The tech had to move it out of the way to pull the radiator/condenser assembly. I expect he pushed it too hard, maybe the plastic is brittle, and broke the reservoir.

    Tough luck, but no biggie. I have spare reservoirs. But reading the manual, the only removal process it describes is to remove the entire inverter, then taking the reservoir off as part of a disassembly process. I can't find a "removal" process for just the reservoir. It looks like the two mounting bolts can be accessed, but the two bolts that seal the fluid port into the inverter would be hard. There's a plastic-framed collection of hoses? fuel line? something between the reservoir and the ICE heads.

    Has anyone replaced just that reservoir? Can I move that plastic assembly out of the way to access the reservoir's bottom bolts without yanking the entire inverter?
     
  17. Tombukt2

    Tombukt2 Senior Member

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    If it's like the generation 2 you should be able to do the three bolts that hold the inverter down to on the painted frame rails and one in the back and then lift the inverter on the side that the reservoir is on and take out the two bolts I believe it too I got one sitting outside upside down I'll look at it in the morning.
     
  18. ronlewis

    ronlewis Active Member

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    Dang, so that means taking the wipers/cowl off to get one of those back inverter bolts. Was hoping to get those two bottom bolts coming from the passenger side by removing the hoses. I'll find out taking the one off I guess.
     
  19. Tombukt2

    Tombukt2 Senior Member

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    Try unbolting the inverter from where it bolts near the headlight where it bolts on the front core support and the little 12 mm in the very back of the inverter that screws into the actuator bracket and mount which you won't have to move the wiper tray for then you may have enough room to lift up on the side of the inverter where the jug is and that little 1 inch lift may allow you to get to the two screws bolts where it screws up to the side of the inverter I have to physically go out and look now because I have a car with this sitting there and I can see very clearly I can't remember if those three bolts undone will give you enough lift to allow you to slide your quarter drive ratchet in there and unbolt the reservoir off the side of the inverter even with that big plastic piece in the wiring harness running over the back edge of the valve cover moved out of the way I'm not sure that would give you enough room but I'll know in just a minute I'm fixing to walk out and take a look at some things and then I got to drive to Fayetteville to look at five generation twos.
     
  20. Tombukt2

    Tombukt2 Senior Member

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    So standing here looking down at my generations to inverter water reservoir It looks like I can get my wrench like a ratcheting combination wrench and or a small quarter inch drive flex ratchet and socket down there to get the three bolts undone there's one on each end of the plastic reservoir at the bottom and there's one right by the little o-ring and hole where the water passes through I have an inverter sitting out on the bench right now I'm looking at and the one sitting in the car assembled and if I had to get the one out of the car right now that's assembled that I'm getting ready to drive to Fayetteville looks like it'll be about a 20 minute job without removing the big plastic that runs across the wiring harness at the end of the valve cover down there near the number for spark plug Good luck my friend doesn't look like it'll be that bad