1UZFEric

So I just filled up and had a chance to pop the hood and take a peek. (I took some pics w/ my phone, but they aren't as clear as yours were, so I won't bother uploading them). BUT.

With A/C on max cold, the actuator arm was fully extended. Although I couldn't quite get a good enough angle for great comparison, it looked to me like it was in about the same position as yours is. As I mentioned yesterday, my A/C is ICE COLD w/ the actuator like this, FWIW. Switched it to max hot and the arm fully retracted into the actuator. Turn the car off and it fully extends to the same position as max. cold.

So there ya go. Maybe over the weekend I can get a better shot of exactly where the arm on the valve is.

t2d2

iTrader: (8)

Thanks, much appreciated. It's definitely a tough angle to see what's going on down there... I had much better luck getting the camera into a spot my head wouldn't fit.

So, that confirms what I assumed, that my actuator and valve are working in the correct fashion. The unknown is still there, however: whether my valve is closing fully or if there's something blocking the last 10% or so.

If that is where it's supposed to be fully extended, then: a) there's no point buying a "new" HCV, and b) I need to figure out my options with the blend doors...

t2d2

iTrader: (8)

I just realized, the moderators have been busy moving and combining threads (three into one, two being related but different items and one being a summary of the other two), so everything above is going to be fairly confusing to follow now unless you re-read it from the start.

I may have just found an answer to the ambient temperature sensor question which was merged into this thread!

While my heater isn't on full blast, the ambient sensor also isn't fully disabled like with that person's broken wires. Mine is simply out of spec, so maybe the percentage difference does indeed throw off the system enough to allow partial heat during cooling. With that info, I'm feeling more assured about buying a new sensor, rather than trying to work through other diagnostic steps first, since it seemed like a bad sensor would work in the opposite direction (see post #4 above).

Too bad the '94 doesn't have the temperature reading on the dash to show what the sensor is pulling in!

t2d2

iTrader: (8)

The new ambient temp sensor arrived yesterday. Actually, it looked to be a refurb; all scratched up and dust accumulation in the space between the sensor and bracket. I tested the old and new sensors side by side and was surprised that: a) the old one was reading perfectly in spec now that it's off the car, and b) the new one is out of spec...

@ 74°:
old = 1.70k
new = 1.41k

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

Both dropped in resistance like they should when heated up, but I'm not sure where I was on the temperature scale. (I re-checked the old one today and it read 1.93k @ 76°, so right in line with yesterday's readings.)

Nevertheless, I put the new one on the car to see if it would make a difference and drove a few miles in 91° weather. On the way out, I measured 62° air at the vents with A/C on medium blast, which seems pretty reasonable. Still, I was measuring 87-111° in the cabin, depending on where I put the probe. (The heat buildup in these cars is insane!) On the way back, after the car sat for an hour, I turned off the A/C and checked temps on MAX COLD. For the first mile, I was getting 88° air at the vents -- pretty close to outside air temp -- but then it quickly climbed to 106* and stayed there the rest of the way.

That's rather conclusive that the cold air is being heated.

Now I have to tackle the tougher diagnosis steps, such as what the computer is seeing/doing, blend door operation, etc. Fortunately, the seller of the ambient temp sensor refunded the purchase (they didn't have any more in stock), so I'm not out anything there since the old one may have been just fine, after all.

t2d2

iTrader: (8)

I worked on removing the room temp sensor yesterday to test it. I wasn't successful in getting the trim cover off, as it felt like it would break before the right side came loose, but I did manage to get at the sensor with the left side of the panel pulled out and unclip it.

Specs:
1.6-1.8k ohms @ 77 degrees
0.5-0.7k ohms @ 122 degrees

@ 96 degrees: 0.86-0.92k
@ 69 degrees: 0.91k

At first glance, that looks pretty iffy. However, in removing the sensor, I was surprised that the side clips near the front of it seem to only be for the internal part of the housing. The sensor slides out but is still connected in the back. So, I'm wondering if those consistent ~0.9k readings are because I'm measuring the resistance of whatever it's wired to? If so, I may need to revisit removing the panel for full access. On the other hand, if you can back probe other stuff and get good readings, wouldn't that be exactly what I'm doing here?

t2d2

iTrader: (8)

The problem may finally be identified! And it would appear to be what I suspected earlier in the thread about the heater control valve not extending the rod (closed) as far as it seemed like maybe it should from some eBay pictures.

This old thread was just linked to today and OLT's post #16 recommended disconnecting the rod from the pivot arm. I didn't know you could do that... I did so and got 87° vent air @ 66° outside air the first half of the test drive, and 86° @ 72° coming back ... much better than the old 113° vent air I was getting!

I'm guessing that means mid-80s is as cool as outside air is going to be coming through the vents (I've never had reason to measure it before on other cars) once warmed by the big V8. With the HCV not fully closed, coolant circulation was bumping it up that extra 20-30°.

So, it looks like I need to replace my HCV.

Here you can see how much further the arm can pivot clockwise once disconnected from the fully extended rod.

aliga

iTrader: (147)

i have one ready to ship, 50 to your door if you need.

t2d2

iTrader: (8)

Thanks, I'll let you know if my other option doesn't materialize. I've had another HCV waiting for me to make a decision on for a couple months now while trying to get confirmation that it was the problem all along.

t2d2

iTrader: (8)

Referring back to post #7, I can now confirm that the "S" on the pivot arm should rotate exactly to that little mark when in full cooling. (Also, it returns to that position when the car is shut off, no matter what the HVAC is set to.)

My replacement HCV arrived today. Unfortunately, after installing it, I discovered that the valve itself leaks at the pivot. I didn't have much light left to work with at that point, but just enough along with flood lights and flashlights to drain the coolant again, remove the new HCV, take my old valve off and attach it to the new actuator, reinstall it, and re-fill the coolant. Hopefully, tomorrow I'll be able to fire it up and: a) have no leaks, and b) have an actuator that extends the valve fully. So much for having a spare valve, though.

With the valve removed, I could see how it works internally by looking down into one of the coolant barbs. When the "S" wasn't rotated fully to the mark, part of the opening through the center piece was still exposed, allowing the connection between the inlet and outlet lines to remain open. Also, I did discover that the old actuator does open up far enough to close off the coolant pass-through, but only with the help of a screwdriver turning the pivot screw. It never wanted to return to that fully extended [rod] position on its own, though.

p.s. Removing that crazy pin/clamp thingy on the lower coolant hose was extremely difficult. Are they all like that from the factory, or did someone modify mine along the way? I was able to press the pin down a little with pliers but nothing could push it fully through. I finally got it off by twisting and prying until it was shredded, and even then there wasn't the slightest hint of that pin wanting to budge to allow the latch to swing open. I replaced it with a simple screw clamp.

t2d2

iTrader: (8)

The partially new HCV appears to have solved the problem. 72° vent air @ ~60° outside air this morning seems pretty reasonable. Out of curiosity, has anyone else measured their SC's vent air compared to outside air to see how much it gets warmed going through the ducts?

ponytail 4

I have a '94 SC400 also and I'm getting the same problem with mine. I thought it was low on R134 but when vacuumed out and refilled it showed that my compressor was weak. Had that changed along with the dryer receiver and still the same, the line out of the compressor is really cold but not going into the cabin. I did the check on the control panel and code 43 came up-Air outlet damper position senor circuit. I posted a thread here but no replies. I wanted to know where the hell it was even located so I could check it out. Maybe yours is the same because the heat blows really hot but the air sucks. In the morning if it's cool outside the air seems to work but not as cold as it used to and as the day gets hotter less cool air comes out the ducts. I took off the relay cover under the hood and removed the "dome light" fuse to clear the codes, waited about 30 seconds and replaced it. I then pressed in the air conditioning control **** (auto) and the REC switch together and then turned the key to on and it did the 4 beeps and then the code 43 came up. I did this procedure a couple of times just to see if the same code would come up and it did. I still don't know where the sensor is but maybe if I google it I may get an answer. Just a thought for your problem too, good luck !!

t2d2

iTrader: (8)

I'm guessing you only read the first post? There were no A/C trouble codes for mine and it turned out to be the heater control valve, so most likely not the problem you're describing unless you have multiple things going on.

xshurikx

Great thread T2D2 i will surely be looking at this on my 300 to see if it extends properly. if it does then i will try to disconnect the valve control and close it myself. if that doesn't work then its probably a bad sensor somewhere also causing this issue. i look at my outside temp gauge and it seems to be off a few degrees anyway.

Nickg89

Do u still have the valve and for what year?

KahnBB6

iTrader: (5)

^^ Nickg89, the factory HCV assembly is the same for all years 1992-2000. You'll be good with any example with a working valve section and working solenoid/electric section.