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how to troubleshoot heater control valve?

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Old 07-13-14, 01:32 PM   #1
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Default how to troubleshoot heater control valve?

'94 SC400, heater works but cold air and A/C blow warmer air than they should. Presumably, the heater control valve isn't working properly and allowing hot coolant to circulate at all times, but I'm stuck at the step of determining which part is the problem. I posted the question here a couple days ago, but it hasn't gotten any attention.

"My vacuum hoses are all new and look to be routed correctly. I did the continuity and ground tests on the heater control valve's VSV and they checked out okay, but I didn't do the blow-through (with and without battery power) test since the port configuration is different than the EGR and fuel pressure VSVs, so I wasn't sure what exactly to check."

Comparing pictures of the Four Seasons #74636 HCV that's recommended as a near-drop in replacement, it looks like the valve itself is the part that the actuator (as detailed here mounts on? If so, the valve itself may not be to blame if the actuator isn't functioning properly with vacuum pressure.

How would I test if coolant is still circulating in cooling mode? Locate the inlet side of the HCV's coolant line and have someone pinch it off while the car is running?

I don't have any HVAC codes stored.

Does the actuator only control where the air is directed? That's what I take from the service manual's AC-30 wording. AC-36 covers the possibilities for when NO cool air comes out, but mine is a matter of the cool air being somewhat warmed. I guess I could check the room temperature sensor (AC-45) and related circuits, but that wouldn't explain the symptoms, would it?

There's talk of bypassing the HCV altogether, which I suppose is one way of isolating coolant recirc from the equation for testing.
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Performance: Alternative BFI (BeeFI?), A/T Solenoid Bypass, M2/Manzo axleback exhaust (awaiting mid-pipe resonator delete), 2-Tone Driver's Seat ("performance" as measured by the butt test).
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Old 07-19-14, 12:49 PM   #2
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Default ambient temperature sensor out of range?

One of the problems on my to-solve list is my cold air doesn't blow particularly cold, including A/C. The heater blows nice and hot and everything modulates properly in between, just the cold air has a warm-ish vibe. Likely possibilities include:

- heater control valve is allowing warm coolant to circulate at all times
- cabin temperature sensor is bad
- ambient air temperature sensor is bad
- wiring faults among any or all of the above

I pulled the ambient temp sensor connector off today -- boy was it a bear to get free, with 20 years of road grime packing the plug in there crazy tight -- and checked the resistance between terminals. The FSM says it should read 1.6-1.8k @ 77 degrees, and mine read 1.36k @ 80 degrees. Probably a bit cooler under the car, so since the voltage is supposed to drop as the temperature goes up (0.5-0.7k @ 122 degrees), the actual ~70-75 degrees in the shade should be higher than 1.8k.

Is that far enough out of range to explain cool air being warmed a bit? I don't have any A/C trouble codes, so I assume the connection itself is okay. And does anyone know where to buy one new? I've found them on eBay (Standard Motor Products #AX168 and OEM #8862524061), AutoZone (Duralast #SU7340), and RockAuto (AIRTEX / WELLS #5S5839), but the pictures are all of the sensor's bracket, not the sensor itself. I imagine they're all just using stock photos, but that's not very reassuring. No luck finding it on Sewell. I may have to just go with a used one and hope it has some life left in it.
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Performance: Alternative BFI (BeeFI?), A/T Solenoid Bypass, M2/Manzo axleback exhaust (awaiting mid-pipe resonator delete), 2-Tone Driver's Seat ("performance" as measured by the butt test).
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Old 07-19-14, 01:28 PM   #3
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Actually, I think those new items are the sensor, not just the bracket. The pictures make it look like something different... The original part has a long sensor that extends forward the length of the bracket, whereas the new ones have a short nub sensor that looks like a receptacle (bad picture angles) for the sensor to plug into. Now to figure out if the brackets are similar enough to line up.
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Performance: Alternative BFI (BeeFI?), A/T Solenoid Bypass, M2/Manzo axleback exhaust (awaiting mid-pipe resonator delete), 2-Tone Driver's Seat ("performance" as measured by the butt test).

Last edited by t2d2; 07-19-14 at 05:12 PM.. Reason: typo
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Old 07-19-14, 05:11 PM   #4
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I'll probably go ahead and order one of the new sensors (too bad the late model LS400 one isn't compatible, it costs a third as much), but I'm puzzled about the meaning of the numbers. Specs:

Resistance
at 25C (77F) : 1.6~1.8k
at 50C (122F) : 0.5~0.7k

My 1.36k at 70-75F should be in the 95F range on the scale, assuming linearity between the "cold" and "hot" specs. I figure my cold air is 10-20 warmer than outside air (seat-of-the-pants estimate), so that discrepancy is somewhat in line with the 20-25 between outside temp and what the resistance indicated. However, if the A/C computer thinks it's warmer outside than it actually is, wouldn't that make it provide colder air, not warmer air? Or does it not follow that sort of logic, and it simply goes haywire when it gets bad info?

With my luck with this car, I'll replace one piece of the equation only to find the next thing down the line is also bad.
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Performance: Alternative BFI (BeeFI?), A/T Solenoid Bypass, M2/Manzo axleback exhaust (awaiting mid-pipe resonator delete), 2-Tone Driver's Seat ("performance" as measured by the butt test).
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Old 07-20-14, 12:06 AM   #5
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I found the OEM part via some cross-listing searches. Officially, it's called a Cooler Thermistor, despite the FSM referring to it as the ambient temperature sensor.

http://lexus.sewellparts.com/oem-cat...C400-1997.html

All three of them (ambient, cabin, and solar sensor?) have the same main part number but different sub-numbers, according to Sewell's listing. At least I know the cabin temp sensor part # now in the likely event it's also bad. Also, part #88625-24061 should be a match for Toyota, so I'll check with the local dealer on Monday if they stock it. (No Lexus dealer nearby.)
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Performance: Alternative BFI (BeeFI?), A/T Solenoid Bypass, M2/Manzo axleback exhaust (awaiting mid-pipe resonator delete), 2-Tone Driver's Seat ("performance" as measured by the butt test).
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Old 07-20-14, 01:29 PM   #6
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I measured temps today with the Amprobe. Ambient sensor disconnected, car warmed up, and going 25 mph: 68 out the window, 86 at the vent (MAX COLD). That's in line with the temperature differential I had been estimating. I'll have to try it again with the sensor plugged in, although I'm not really looking forward to wrestling with it again when it comes time to replace it.

I still think it's going to end up being an issue with the heater control valve...
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Performance: Alternative BFI (BeeFI?), A/T Solenoid Bypass, M2/Manzo axleback exhaust (awaiting mid-pipe resonator delete), 2-Tone Driver's Seat ("performance" as measured by the butt test).
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Old 07-20-14, 03:21 PM   #7
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It occurred to me today that I can see the valve's (actuator) operation by either using a mirror or peering below it at a shallow angle, and testing its range of movement in MAX HOT or MAX COLD. Attached are two pics of it, looking horizontally from the passenger fender; the first one heating and the second one cooling.

Does that seem like the proper range for the lever, and is it moving in the right direction? The only picture/explanation I could find to that effect is step #12 of the lexls radiator flush LS400 guide. The HCV isn't positioned the same there, so I'm not sure if it's an apples and oranges comparison, but "make sure that the heater control valve is fully open" for max heat seems the opposite of what mine is doing. Mine looks closed, but maybe the fully recessed arm is actually considered open?

Also, I noticed there are notches on the bracket that rotates around the screw, and the MAX HOT one lines up pretty closely with the arrow. There's also that little notch above the "S" in the MAX COOL pic, but the arrow only rotates halfway there. Should it be rotating far enough to hit that mark? I can rotate it the other direction (pushing the arm into the actuator) with some force, but it seems locked out going more toward the little notch.

If that's all as it should be, then I've also been reading up on the possibility of a stuck (or defective) blend door and whether that can be serviced by spraying cleaner in there to work its way through the system.
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Performance: Alternative BFI (BeeFI?), A/T Solenoid Bypass, M2/Manzo axleback exhaust (awaiting mid-pipe resonator delete), 2-Tone Driver's Seat ("performance" as measured by the butt test).
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Old 07-20-14, 05:24 PM   #8
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I looked through most of the HCVs listed on eBay and found a few with pictures correctly oriented for comparison. I'm pretty sure my actuator isn't pushing the rod far enough out in MAX Cool. From the picture above, you can see the bracket aligns almost perfectly with the square-ish front corner of the valve. From the pictures I found, it appears it should go slightly past that corner.

I'm still trying to make sense of this suggestion from another site:

Quote:
The control valve is known for leaking. Also have someone press temp. up and then down while you monitor the valve, see if the cable attached to it moves, you may need to spray wd=40 or another penetrating oil down the cable guide tube, what usually hapens with this car is the heater control valve starts to develop a small leak, it drips on the cable and eventually rusts the cable solid in place. This cable is what opens the heater control valve and allows heat to enter the heater control valve. If the cable will not move then disconnect it, open the heater control valve by hand and now test the heat. Most likely if the cable was seized the heat will now work and you will need to replace the cable and the heater control valve.
Any idea what cable he is referring to? The only thing I can figure is that's the rod that I've been describing, i.e. a cable as in a linkage. But then, what's the cable guide and how would you spray WD-40 down it when it fact the rod moves up? Is he talking about the vacuum port on top?? Or is the cable guide what I've been calling the bracket? Or maybe just teh screw itself? I don't have any signs of rust, so it may be n/a. Also, how would you disconnect the cable (rod)? It has some sort of a fastener on the back that looks like it isn't supposed to be removed, but maybe it's just a tiny rubber cap that pops off.

I realize we're not supposed to post eBay links, but obviously this a diagnostics question and not a veiled sales attempt. Here are two of the better pictures I found, showing the rod extended more fully than mine:

http://i.ebayimg.com/00/s/MTIwMFgxNj...ykw~~60_57.JPG

http://i.ebayimg.com/00/s/MTI3NVgxNj...SxOM0/$_57.JPG

Edit: The open/close confusion is probably because of the inconsistent usage of valve vs actuator. The open position of the actuator (extended arm) would be the closed position of the valve.
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'94 SC400 Factory Frankenstein: '00 RX300 steering wheel, '93-96 GS300 speedo/tach needles, '98-02 GS4xx wheels, Prius lug nuts (eco friendly!) ... LS400 calipers denied wheel clearance for take-off.
Performance: Alternative BFI (BeeFI?), A/T Solenoid Bypass, M2/Manzo axleback exhaust (awaiting mid-pipe resonator delete), 2-Tone Driver's Seat ("performance" as measured by the butt test).

Last edited by t2d2; 07-20-14 at 11:42 PM..
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Old 07-21-14, 09:35 PM   #9
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Bump. Surely, someone has a SC sitting around with a working heater control valve in the MAX COLD position to see where the actuator arm and bracket line up?
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Performance: Alternative BFI (BeeFI?), A/T Solenoid Bypass, M2/Manzo axleback exhaust (awaiting mid-pipe resonator delete), 2-Tone Driver's Seat ("performance" as measured by the butt test).
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Old 07-23-14, 07:44 AM   #10
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Default duplicate post, can't get any answers to warm-ish cold air...

I posted both of these in the Performance & Maintenance forum, thinking that was the appropriate place, but nary a response in 10 days... Just need some simple Yes/No answers before I go buying parts. My cold air (with or without A/C) is warmed 10-20 at the vents. I have two likely culprits:

1) Heater Control Valve - http://www.clublexus.com/forums/perf...rol-valve.html

Post #2: Is my HCV Actuator extending the arm fully enough to close the valve and cut off coolant circulation, or should the bracket be rotating further to line the arrow up with the smaller notch?

2) Ambient Temperature Sensor - http://www.clublexus.com/forums/perf...-of-range.html

My sensor's resistance read 1.36k @ 70-75 (in the shade), whereas specs call for 1.8k+ at that temperature. Is that far enough out of spec to explain the warming of the cold air?

Also, combining thoughts from the two topics, could the ambient sensor being out of range force the HCV to not fully close? I wouldn't think they interact in that manner, but I've found precious little info on either, other than non-applicable "bypassing the HCV" stuff for when the heater doesn't work. My heat works fine.

Thanks in advance for any and all responses.
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Performance: Alternative BFI (BeeFI?), A/T Solenoid Bypass, M2/Manzo axleback exhaust (awaiting mid-pipe resonator delete), 2-Tone Driver's Seat ("performance" as measured by the butt test).
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Old 07-23-14, 08:02 AM   #11
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Opening a new thread for the same issue, in the wrong section is frowned upon but hey, I'm not the admin.

Is it like that at all times? I know mine is really cold while moving but stopped at a light it starts to blow humid warm air instead, obviously not getting air through the condenser will change things but that's where the clutch/fan and shroud come in so you should make sure those are working and there too.
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Old 07-23-14, 08:09 AM   #12
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Yes, it's like that at all times. Temperatures modulate between Hot and Cold properly, just they're moved up the scale from the Cold end of the range. I've read temps while moving and while stopped, and the inside/outside differential is pretty consistent.

I wouldn't normally open a duplicate topic, but: A) I put that first thing in the title, B) I think I've waited plenty long for a response to the other topics, and C) the Performance & Maintenance forum seems to be more about the Performance than the Maintenance, so I'm not so sure that was the best place to post them.
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Performance: Alternative BFI (BeeFI?), A/T Solenoid Bypass, M2/Manzo axleback exhaust (awaiting mid-pipe resonator delete), 2-Tone Driver's Seat ("performance" as measured by the butt test).
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Old 07-24-14, 12:01 PM   #13
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I'm currently sittin at my desk, so I can't go look, but IIRC from messing with mine, the actuator's "default" position is down (i.e., w/ no vacuum applied, the arm is fully extended), which results in full heat. I never got the impression that the control valve has the ability to be anything but fully open or fully closed; much rather, the blend doors do the work of directing more/less air through the heater core, which results in more/less heat coming out the vents.

Might be a stupid question, but have you considered the possibility that your car is low on refrigerant?...

As for what the other member was talking about lubricating a cable, surely that was in reference to another vehicle; I think that on alot of older (and probably to some extent, newer, less complicated cars), the heater valve (and most of the HVAC controls, for that matter) were controlled via cables. The Lex, I'm pretty sure, is all vacuum and/or servo-controlled.

If I can remember, I'll pop my hood when I leave this afternoon and check mine out for ya.
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Old 07-24-14, 12:02 PM   #14
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i have a valve if you need, 40 shipped
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Old 07-24-14, 12:13 PM   #15
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Quote:
Originally Posted by 1UZFEric View Post
I'm currently sittin at my desk, so I can't go look...
Although not an immediate resolution, you just made my day! Been holding my breath for a response of some sort...

Quote:
but IIRC from messing with mine, the actuator's "default" position is down (i.e., w/ no vacuum applied, the arm is fully extended), which results in full heat.
I think it's the other way around. I tested it with the VSV bypassed, which should result in full coolant circulation, and that moved the actuator arm all the way in.

Quote:
I never got the impression that the control valve has the ability to be anything but fully open or fully closed; much rather, the blend doors do the work of directing more/less air through the heater core, which results in more/less heat coming out the vents.
That's exactly why I'm trying to determine if the HCV is functioning as it should. The blend doors don't sound like much fun to work on, if they turn out to be the issue. Although, I haven't found much SC-specific on that; mostly general tips on trying to work some sort of cleaner down from the defrost vents through the system.

It just seems from the marks on the HCV's pivot that it isn't extending the bracket as far as it ought to.

Quote:
Might be a stupid question, but have you considered the possibility that your car is low on refrigerant?...
It's topped off.

Quote:
As for what the other member was talking about lubricating a cable, surely that was in reference to another vehicle; I think that on alot of older (and probably to some extent, newer, less complicated cars), the heater valve (and most of the HVAC controls, for that matter) were controlled via cables. The Lex, I'm pretty sure, is all vacuum and/or servo-controlled.
That would make sense, but it was an "expert's" answer to a '93 SC400, and I've found that site to be pretty accurate with parts and diagrams.

Quote:
If I can remember, I'll pop my hood when I leave this afternoon and check mine out for ya.
Thanks! I figure in mid-summer, most everyone's HCV is sitting in the MAX COLD position, so no need to even start the car to check.

Quote:
Originally Posted by aliga View Post
i have a valve if you need, 40 shipped
That's a good price, thanks. I do already have one lined up with a CL'er for about the same price ... been holding that up for the past week while I try to get an answer as to whether that's actually the issue.
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Performance: Alternative BFI (BeeFI?), A/T Solenoid Bypass, M2/Manzo axleback exhaust (awaiting mid-pipe resonator delete), 2-Tone Driver's Seat ("performance" as measured by the butt test).
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