Heater blows cold while driving, hot at idle.

[vigness]

I had mine wired for about three months until spring. That was the first one with the paper instructions.

For the second one, between having done it and realizing how simple it was and a couple of good YouTube videos, I just waited for a calm sunny day and did it.

Of course they both had to fail in the winter. Couldn't have happened in the summer where I could just have hit it early before the temps jumped up... Noooooo, that would be too easy.

 

[smythcounty]

Delete

 

[smythcounty]

So I flushed the heater core and got a good steady stream coming out of both sides. I reversed the hoses and refilled the coolant level. Check temp with obd2 scanner and showed 190 degrees. The top heater core hose going through the firewall is hot and the bottom one is still cold. I had to manually open the heater control valve, no longer works with the vacuum, maybe I got a bad one when I replaced it in the summer? I can hear the blend door moving or maybe the actuator when moving the temp knob from hot to cold. The air does get a little colder when I turn it to cold but maybe only a degree or two different. I noticed I don’t get any pressure on the radiator. I can remove the cap and there is no pressure. Related? I don’t now. Just seems strange. Next step this evening is to replace the heater control valve. Thanks for all the suggestions, any other ideas would be appreciated.

 

[James Morse]

You keep saying the heater control valve doesn't open with vacuum, but unless I'm misunderstanding what Ron D said, it should be open if there is no vacuum. Vacuum closes it. So it seems to me like if you had no vacuum it would be always open (unless it's a p.o.s.) To repeat, vacuum closes it only if selector is on Max AC or Off. Surely someone on here knows and can confirm/deny that.

As to no pressure, I'd check/replace the radiator cap. That's where the pressure relief valve is. If it's failed, it could let coolant go to the overflow tank at low pressure thus causing what you report. But you'd still get heat if the coolant is hot, so, two different problems. I doubt replacing radiator cap would have any effect on the heat problem. But it's cheap ($10 +/-) and 5 seconds to change so I'd do that first.

Just to be clear, I'm no expert on this... just following what seems logical. The h.c.v. has to be spring-loaded to return it to open at no vacuum, so if yours sticks closed, it sounds like it's trash. It would make sense that the default would be open, because you can live with the core active even when using AC, but if the default (no vacuum) was closed, and it failed, then you have no heat, and can't pass inspection, if you have that, not to mention it's a nightmare in winter. Mine, with engine off (no vacuum), if I push a bit on it, it springs right back to, I assume, open. So, loss of vacuum, if it were that problem, would cause it to be always open. Sounds to me like yours has a broken/failed spring and if it gets closed, it stays closed... guessing... mine's different because as I said before it's only on one hose, but in operation they should be similar. What I'm saying is, if you can move it back and forth by hand and it doesn't return to its home position (open) then that's not how it's supposed to work so it's crap.

I suppose you could take the heater control valve right out of there and (with connectors) just connect the hoses, that would tell you for sure if it's that or not. The only downside to that is you'd have hot coolant going thru the core on Max AC and Off, but I don't see that would cause any particular problem except at Off you'd have perhaps some heat build-up around the core... probably wouldn't matter. I would imagine the reason it works the way it does is that even when AC is on (not Max AC), you still want the heater core active because sometimes you just want mild cooling.

I'm sure some big guns on here will chime in as to whether what I'm telling you is good info.

 

[smythcounty]

You keep saying the heater control valve doesn't open with vacuum, but unless I'm misunderstanding what Ron D said, it should be open if there is no vacuum. Vacuum closes it. So it seems to me like if you had no vacuum it would be always open (unless it's a p.o.s.) To repeat, vacuum closes it only if selector is on Max AC or Off. Surely someone on here knows and can confirm/deny that.

As to no pressure, I'd check/replace the radiator cap. That's where the pressure relief valve is. If it's failed, it could let coolant go to the overflow tank at low pressure thus causing what you report. But you'd still get heat if the coolant is hot, so, two different problems. I doubt replacing radiator cap would have any effect on the heat problem. But it's cheap ($10 +/-) and 5 seconds to change so I'd do that first.

Just to be clear, I'm no expert on this... just following what seems logical. The h.c.v. has to be spring-loaded to return it to open at no vacuum, so if yours sticks closed, it sounds like it's trash. It would make sense that the default would be open, because you can live with the core active even when using AC, but if the default (no vacuum) was closed, and it failed, then you have no heat, and can't pass inspection, if you have that, not to mention it's a nightmare in winter. Mine, with engine off (no vacuum), if I push a bit on it, it springs right back to, I assume, open. So, loss of vacuum, if it were that problem, would cause it to be always open. Sounds to me like yours has a broken/failed spring and if it gets closed, it stays closed... guessing... mine's different because as I said before it's only on one hose, but in operation they should be similar. What I'm saying is, if you can move it back and forth by hand and it doesn't return to its home position (open) then that's not how it's supposed to work so it's crap.

I suppose you could take the heater control valve right out of there and (with connectors) just connect the hoses, that would tell you for sure if it's that or not. The only downside to that is you'd have hot coolant going thru the core on Max AC and Off, but I don't see that would cause any particular problem except at Off you'd have perhaps some heat build-up around the core... probably wouldn't matter. I would imagine the reason it works the way it does is that even when AC is on (not Max AC), you still want the heater core active because sometimes you just want mild cooling.

I'm sure some big guns on here will chime in as to whether what I'm telling you is good info.

Thanks for the info. When I say it stopped working on vacuum, i meaning that it’s not operating either way, opening or closing. I’m having to manually open and close it, so it’s defective in that way, not sure if that is still causing the problem though. It’s covered under warranty, so I’m going to change it since it only takes a couple minutes.
I’m debating on changing the thermostat just to rule out anything else, but it seems like it’s a pain to change.
Anyways I’ll keep the board updated.
Thanks!

 

[James Morse]

I checked mine, and like I said it's spring-loaded, under no vacuum it is always open. Off and Max AC move it closed. So it works just like Ron D said (of course). Sounds like spring is shot on yours.

T-stat not hard to change. Take off air tube, not mandatory, but makes it a lot easier and very quick to do. Trash old t-stat, clean off any Permatex, crap, etc where it mounts, and put in new one with the gasket that you purchase (separately) at time you get the t-stat. I doubt that has anything to do with the heat problem, but if this is a 'new' vehicle might be nice to do it just so you have new 190-195 one in there.

If you know what is the open position on the h.c.v. you could tape or wire it open that should tell you something - meaning, you should have heat. In fact, quick and dirty would be just do what I said and drive thru the winter like that, you'll never be using Max AC or Off anyway. Obviously that's a kluge. But since changing it out is a matter of a few minutes, I'd take the thing back and show them, it doesn't return to its home position (open), it's junk.

Kind of makes sense you could have heat when you move it open by hand and truck is sitting in driveway then you drive and it moves closed by itself from vibration/coolant flow/ whatever (no spring) then you lose heat. See? Again, default is that it should be always open, even with engine off it's open because spring forces it to be open. The fact you can move it back and forth by hand and it doesn't return to open position is the tell.

 

[smythcounty]

I checked mine, and like I said it's spring-loaded, under no vacuum it is always open. Off and Max AC move it closed. So it works just like Ron D said (of course). Sounds like spring is shot on yours.

T-stat not hard to change. Take off air tube, not mandatory, but makes it a lot easier and very quick to do. Trash old t-stat, clean off any Permatex, crap, etc where it mounts, and put in new one with the gasket that you purchase (separately) at time you get the t-stat. I doubt that has anything to do with the heat problem, but if this is a 'new' vehicle might be nice to do it just so you have new 190-195 one in there.

If you know what is the open position on the h.c.v. you could tape or wire it open that should tell you something - meaning, you should have heat. In fact, quick and dirty would be just do what I said and drive thru the winter like that, you'll never be using Max AC or Off anyway. Obviously that's a kluge. But since changing it out is a matter of a few minutes, I'd take the thing back and show them, it doesn't return to its home position (open), it's junk.

Kind of makes sense you could have heat when you move it open by hand and truck is sitting in driveway then you drive and it moves closed by itself from vibration/coolant flow/ whatever (no spring) then you lose heat. See? Again, default is that it should be always open, even with engine off it's open because spring forces it to be open. The fact you can move it back and forth by hand and it doesn't return to open position is the tell.

I just realized I posted in wrong forum. If a mod wants to move it that’d be great.
I swapped heater control valve with a new replacement and went ahead and flushed the heater core again just to be on the safe side. And voila, I have heat at idle, but I must’ve gotten water on something because the truck won’t stay running and I get misfires on all 6 cylinders. What an idiot. I knew better.

 

[James Morse]

Water on something like distributor? I'm really at a loss. If you put a hose on the core when flushed it should have kept water away from stuff. Wipe things off, or let it dry? A different problem?
Well, when it gets sorted, I know this, if you nailed the heater problem, you'll thank yourself every time you get nice heat for whatever time and effort it took.