Weird heater control valve behavior?
06-09-2017, 01:53 AM
#1
Rennlist Member
Thread Starter
Weird heater control valve behavior?
As I supposed, my HCV is bad. Seems the diaphragm is bad, didn't close even with direct vacuum. The new one closed fine tested with the same line. I got all my old lines replaced with new silicone lines, and hooked up the new one in a place I could see it operate to make sure the control unit and vacuum actuator were functioning normally. My results were mixed.
First of all, nothing I did with the temp **** changed anything. It stayed open. The only things that closed it were hitting the A/C switch or the recirculation button. Both those closed the HCV no matter where the temp control **** was.
One weird thing here is that from what I'm seeing I can never have heat if I have recirculation on (button pressed in, light on) but it also means I'll always have some heat if I have it pulling outside air.
My temp **** does control the mix door, and it does maintain the set temp correctly. So the unit seems to be functional. But something doesn't seem right in the control of the HCV. I don't see why the recirculation button would close the HCV irregardless of temp setting, and I would have expected full cold temp setting to close it as well.
Is there a factor I'm missing here? I did let it idle till it was blowing hot air, but it wasn't up to normal temp yet. Will it act differently once warmed up fully??
Any ideas? I'll test more tomorrow, but I'm a little stumped.
First of all, nothing I did with the temp **** changed anything. It stayed open. The only things that closed it were hitting the A/C switch or the recirculation button. Both those closed the HCV no matter where the temp control **** was.
One weird thing here is that from what I'm seeing I can never have heat if I have recirculation on (button pressed in, light on) but it also means I'll always have some heat if I have it pulling outside air.
My temp **** does control the mix door, and it does maintain the set temp correctly. So the unit seems to be functional. But something doesn't seem right in the control of the HCV. I don't see why the recirculation button would close the HCV irregardless of temp setting, and I would have expected full cold temp setting to close it as well.
Is there a factor I'm missing here? I did let it idle till it was blowing hot air, but it wasn't up to normal temp yet. Will it act differently once warmed up fully??
Any ideas? I'll test more tomorrow, but I'm a little stumped.
06-09-2017, 05:10 AM
#2
Rennlist Member
Thread Starter
More testing showed that with the A/C on, the valve worked as I would expect. Set to cold it closed, set to hot it opened. This is however how I would expect it to always work.
Recirculation on, it's always closed, A/C on or off. Temp hot or cold.
Recirculation off, A/C off. It's always open.
Something weird I've noticed before, with recirculation on it never blows near as hot. That was with my broken HCV that's stuck open. The best I ever get with recirculation pressed is warm air. I get hot if I turn it off. That kinda follows what I'm seeing from the working HCV. But I don't see why it would be this way by design.
If anything, I would rather have it reversed. I like cool outside air in the evenings. But what I get is warm air, even set to cold. The middle vents are cool, but the floor vents blows warm, and so do the side vents. That's with the setting all the way cool. I had been hoping it was due to my bum HCV. But it seems it will be doing the same thing with the working one....
But, at least my A/C will be working better!!!! So I guess I'll just have to count my blessings.
Recirculation on, it's always closed, A/C on or off. Temp hot or cold.
Recirculation off, A/C off. It's always open.
Something weird I've noticed before, with recirculation on it never blows near as hot. That was with my broken HCV that's stuck open. The best I ever get with recirculation pressed is warm air. I get hot if I turn it off. That kinda follows what I'm seeing from the working HCV. But I don't see why it would be this way by design.
If anything, I would rather have it reversed. I like cool outside air in the evenings. But what I get is warm air, even set to cold. The middle vents are cool, but the floor vents blows warm, and so do the side vents. That's with the setting all the way cool. I had been hoping it was due to my bum HCV. But it seems it will be doing the same thing with the working one....
But, at least my A/C will be working better!!!! So I guess I'll just have to count my blessings.
06-10-2017, 02:12 AM
#4
Rennlist Member
Thread Starter
But I don't WANT it to work that way!!! 
Can anyone verify when theirs opens and closes???
Once off, verified that in fact the vacuum diaphragm was toast. You could suck air right through it. Seemed to be the original, it was in really sorry shape, good thing I replaced it!!!!
Anyway got it done today, and here's my tips.
Use 3mm silicone hose. I used 2mm, and it worked for all but 2 fittings. Had to rig up those with some 3mm I had and the original hard lines. Works, but would have rather had it all 3mm.
I was relieved to discover my 951 radiator had a drain plug. My 87 NA doesn't. Got under there, got my bucket all ready, undid the plug, and got a squirt, then nothing. I was thinking maybe it was stopped up, had that happen before. Was getting ready to try and figure it out when coolant started pouring down on my head.... It had ran down the mounting rail and came out the other end. On my head.
Two things here, first just keep this in mind and don't be me. Second, if you take the radiator cap off FIRST, it will shoot out like your expecting. You'll still get coolant come out along the rail, but you should have time to get out from under it first!
The HCV was a snap to do. Took like 15 minutes. I undid the top house from the block, then moved wires and hoses aside till I could work it up on top, pulling it out over closer to the battery. The bottom hose is plenty long enough. Once up on top, I had full access to both hoses. Easy to get the old one off and the new one all hooked back up. Then just pushed it back down through the "opening" I'd made, hooked it back into the neck on the block and was done.
Took me 3x as long to get the vacuum hose hooked back to it!!! That was the true pain!!!!
Well that, and burping the system. Once I had it all back together I started it up to start burping it. Even after 15 mins my heater was still blowing cold. Ended up taking it for a drive. Didn't get heat till I opened it up to 5-6K a couple of times. Then hit the highway and ran it at 4k for miles. Finally started to get some real heat. Thought I had all the air out, but as soon as I stopped to turn around it went cold again. Crap!
On the way back, after 4 miles at highway speed, started getting good heat again. Got home and popped the hood, bled it out the "bleed screw" again and got lots of air, then finally water. Checked the overflow, it was almost empty!!! That was a LOT of air. Checked several times, no leaks. Kept filling and bleeding for a bit (was still running this whole time) but the heat started going cold again!! WTH! And yes, I verified my new HCV was full open this whole time!
Ended up driving it again, getting heat again, then burping again. Heat didn't stay as hot as I'd of liked, but it was much better. Couldn't get any more bubbles out. Gave up for now.
Parked it nose up in my super steep driveway, will burp again tomorrow. But I think in going to have to do a pressure burp on it!! It's being a total pain!!!!
Can anyone verify when theirs opens and closes???
Once off, verified that in fact the vacuum diaphragm was toast. You could suck air right through it. Seemed to be the original, it was in really sorry shape, good thing I replaced it!!!!
Anyway got it done today, and here's my tips.
Use 3mm silicone hose. I used 2mm, and it worked for all but 2 fittings. Had to rig up those with some 3mm I had and the original hard lines. Works, but would have rather had it all 3mm.
I was relieved to discover my 951 radiator had a drain plug. My 87 NA doesn't. Got under there, got my bucket all ready, undid the plug, and got a squirt, then nothing. I was thinking maybe it was stopped up, had that happen before. Was getting ready to try and figure it out when coolant started pouring down on my head.... It had ran down the mounting rail and came out the other end. On my head.
Two things here, first just keep this in mind and don't be me. Second, if you take the radiator cap off FIRST, it will shoot out like your expecting. You'll still get coolant come out along the rail, but you should have time to get out from under it first!
The HCV was a snap to do. Took like 15 minutes. I undid the top house from the block, then moved wires and hoses aside till I could work it up on top, pulling it out over closer to the battery. The bottom hose is plenty long enough. Once up on top, I had full access to both hoses. Easy to get the old one off and the new one all hooked back up. Then just pushed it back down through the "opening" I'd made, hooked it back into the neck on the block and was done.
Took me 3x as long to get the vacuum hose hooked back to it!!! That was the true pain!!!!
Well that, and burping the system. Once I had it all back together I started it up to start burping it. Even after 15 mins my heater was still blowing cold. Ended up taking it for a drive. Didn't get heat till I opened it up to 5-6K a couple of times. Then hit the highway and ran it at 4k for miles. Finally started to get some real heat. Thought I had all the air out, but as soon as I stopped to turn around it went cold again. Crap!
On the way back, after 4 miles at highway speed, started getting good heat again. Got home and popped the hood, bled it out the "bleed screw" again and got lots of air, then finally water. Checked the overflow, it was almost empty!!! That was a LOT of air. Checked several times, no leaks. Kept filling and bleeding for a bit (was still running this whole time) but the heat started going cold again!! WTH! And yes, I verified my new HCV was full open this whole time!
Ended up driving it again, getting heat again, then burping again. Heat didn't stay as hot as I'd of liked, but it was much better. Couldn't get any more bubbles out. Gave up for now.
Parked it nose up in my super steep driveway, will burp again tomorrow. But I think in going to have to do a pressure burp on it!! It's being a total pain!!!!
06-10-2017, 07:39 AM
#5
Recirculation is basically maximum A/C. Most cars are set up this way. Sounds normal to me.
When bleeding the cooling system the recirculation should be off and set to the highest temperature settings or you may be leaving air in the heater core.
Try bleeding the cooling system with the coolant filled right to radiator cap and maintain the coolant level ABOVE the maximum line on the coolant reservoir. I find this really helps with bleeding and keeping the air out.
When bleeding the cooling system the recirculation should be off and set to the highest temperature settings or you may be leaving air in the heater core.
Try bleeding the cooling system with the coolant filled right to radiator cap and maintain the coolant level ABOVE the maximum line on the coolant reservoir. I find this really helps with bleeding and keeping the air out.
10-30-2018, 03:31 PM
#6
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My heating is driving me nuts right now (1986 2.5 lux) with being on hot the whole time! Ive gone through the system as best I can and worked out the following:
Only thing I can think is that the heater rheostat is broken on my new 2nd hand heater control unit - Ive tried 3 now so would be damn unlucky if I had 3 failed units? Either that or theres no +ve feed coming in to the rheostat that shuold then go out to the solenoid when the temp control is set to cold? As far as Im aware there are no hidden fuses anywhere to check..
Any help appreciated as Im not sure what to do next and cant afford to keep buying heater control units!
- tested vacuum valve in engine bay - works fine if I suck on it or if I bypass the internal pipes and hook the brake vacuum directly to it
- swapped out both solenoid valves under dash
- swapped out heater control unit with a 2nd hand one and now when I hit the recirc button I can feel the rear solenoid work and recirc circuit works properly
- no matter what I do with the heater **** it just blows hot air constantly - solenoid doesnt feel like its switching at all
Only thing I can think is that the heater rheostat is broken on my new 2nd hand heater control unit - Ive tried 3 now so would be damn unlucky if I had 3 failed units? Either that or theres no +ve feed coming in to the rheostat that shuold then go out to the solenoid when the temp control is set to cold? As far as Im aware there are no hidden fuses anywhere to check..
Any help appreciated as Im not sure what to do next and cant afford to keep buying heater control units!
10-30-2018, 03:59 PM
#7
Nordschleife Master
Full heat on the later (85.5+) cars is usually a broken simple plastic clip that supports a metal rod under the drivers side dash. It’s cheap and easy to replace or use a cable tie as a temporary measure to attach the rod back in place.
Look under the drive side dash and see if you can see a detached metal rod hanging there, that will be your problem.
Look under the drive side dash and see if you can see a detached metal rod hanging there, that will be your problem.
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10-30-2018, 04:18 PM
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Full heat on the later (85.5+) cars is usually a broken simple plastic clip that supports a metal rod under the drivers side dash. It’s cheap and easy to replace or use a cable tie as a temporary measure to attach the rod back in place.
Look under the drive side dash and see if you can see a detached metal rod hanging there, that will be your problem.
Look under the drive side dash and see if you can see a detached metal rod hanging there, that will be your problem.
10-30-2018, 04:50 PM
#9
Nordschleife Master
10-30-2018, 05:34 PM
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