Heater Control Valve

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

6DollarRooster

6DollarRooster

10 Year
Joined
Feb 12, 2012
Threads
14
Messages
85
Location
Alaska
I've done some searching but can't find the answers to my questions.

'97 LX with 165k on the clock.

Last winter my heater didn't work so well. And it's still not working so well and I suspect it could be my heater control valve. I did a very thorough coolant flush/heater core flush this summer and had 140*+ air coming out of the vents at idle while I was cleaning it. I got a lot of nasty rust colored coolant that I suspect came out of the heater core out too. Now that it's starting to freeze up here in Alaska, my heater is luke warm again. As far as I can tell, the valve is original Denso. It probably needs to be switched out (or at least a backup bought) but how can I tell if it's working properly? With the engine warm and switched to full heat I'm getting 175*-180* on the drivers side and 10* cooler on the passenger side. With it switched to cool, both sides are 175*-180*. What should the temperature differential be side to side with a working valve? Can I get a pic of a working valve set on full heat? Pic of one on full cool? Thanks for your help...

Rick
 
Does your fan blow ?

Your valve is mounted under the hood on the fire wall. Seems you should be able to visually look at the cable/plunger at the coolest setting, then push to the hot, and look again and see if it's moved.
 
I know exactly where it's located. I've inspected it. It's 12v activated but what's fully open look like and what's fully closed? Does anyone know the temp differential I should be getting if it's fully closed?

Thanks
 
AFAIK with the OEM valve closed a small amount of hot water will still circulate in the front and rear heater cores, but only a trickle, not enough to give you that high a temperature coming out of the vents.

Closed should be with the exposed section of cable being at it's shortest, open would be with more of the cable exposed (extended) out of the sheath, if that makes sense.

You can slide the cable off the heat valve lever, then push the lever fully closed, which should be down or more horizontal IIRC. Is the cable attached to the lever of the valve, and does the cable move in and out when you adjust the HVAC heat controls?
 
Last edited:
My heat didn't work well either. This is on e '93, so I'm not 100% sure it is the same on your '97. Anyhow, I took off the cable controlling the heater control valve and manually opened up the valve. Still no heat. So I took out the valve to see if it was opening / clogged. The valve was OK.

Turns out that the solenoid that opens the heater control valve also opens a flapper valve that directs the air over the heater core. For me, the flapper wasn't opening, so no air over the heater core and thus no heat. It turned out to be a bad / cold solder joint on the heater temp slider. HTH.
 
i believe the general rule for the HCV is if you have to even mention it - replace it....

the plastic on the OEM erodes naturally erodes over time - so i would not recommend
inspecting it or loosening it from the hoses - (lest you have a spare one on hand) -

there are indeed plenty of horror / limp home stories (mine included) - and for $40 from Autozone -
it is a good / cheep PM (stealership wants $150 and would take a week to special order)

Bf
 
Thanks Kernal, your description helps. I'll take a look.

Cruzerman, that's real interesting about solenoid. Anyone know where I could inspect that flapper that he mentioned on a '97?

Baselfish, I'll be picking one up shortly as a spare for sure.

Thanks
 
Cruzerman said:
My heat didn't work well either. This is on e '93, so I'm not 100% sure it is the same on your '97. Anyhow, I took off the cable controlling the heater control valve and manually opened up the valve. Still no heat. So I took out the valve to see if it was opening / clogged. The valve was OK.

Turns out that the solenoid that opens the heater control valve also opens a flapper valve that directs the air over the heater core. For me, the flapper wasn't opening, so no air over the heater core and thus no heat. It turned out to be a bad / cold solder joint on the heater temp slider. HTH.
Click to expand...

My heater is doing exactly this. HCV is brand new. Is it possible to manually open the "flapper" to the heater core? Where is it located?
 
Yeah, you must be looking at the wrong thing. The heater valve is not 12v activated, it is cable activated. Please read the previous posts on location. You can't visually inspect the flapper without removing it. And make sure that you have a new one before you do.
 
Thanks guys - my question isn't about the heater control valve on the firewall under the hood. I'm looking for the before mentioned "flapper" that allows air to move over/through the heater core. I think this is the problem my 80 is having. The HCV is open, but no hot air. I'd like to check whether the heater core is allowing warm air to the vents.
 
Hot air? There should be coolant moving through there, unless I'm misunderstanding you?

If you want one that closes or opens all the way, but the four seasons one from rock auto.
 
Are you speaking of the air damper? I believe that all that does is switch the air flow from defrost, to feet to main vents. It's still blowing across the heater core. Are you getting good heat from your rear heater under passenger seat?
 
Last edited:
AMX390 said:
Are you speaking of the air damper? I believe that all that does is switch the air flow from defrost, to feet to main vents. It's still blowing across the heater core. Are you getting good heat from your rear heater under passenger seat?
Click to expand...

Is the guy in your avatar taking a dump?
 
Seems I've successfully hijacked this thread.

Cruzerman mentioned this:
Cruzerman said:
Turns out that the solenoid that opens the heater control valve also opens a flapper valve that directs the air over the heater core. For me, the flapper wasn't opening, so no air over the heater core and thus no heat.
Click to expand...

His explanation sounds like the same issue I'm experiencing. Hot coolant moving through the HCV, but no hot air through the vents.

I've never gone deep enough into the dash to know where I'd find this air "flapper". How can I check to see if air is being allowed through the heater core?

The floor/vent/defrost control is working fine. Except that the air coming out is not warm.
 
Last edited:
Not trying to thread hijack, but I'm also having heater issues on my 97 LX450. No matter what state my (auto) HVAC controls are set to my vents always blow ambient temperature at best (although AC definitely works and blows cold.)

I left the radiator cap off with the truck at a slight incline in my driveway (not sure the cap opening was higher than the rear valve on the firewall to be quite honest) for 20 minutes or so and nothing. Also checked rear heat - the rear heat fan definitely works, but again blows cold/ambient.

I put my hand on the driver's side metal pipe (is that the PHH?) going up into the hose that connects to the regulator valve on the firewall, and it was getting warm/hot, but I didn't feel any significant heat on the passenger side of the valve.

Would that be the first thing you guys replace?
 
sounds to me like the HCV - again cardinal rule - don't fux wit it lest you are
prepared to replace it...

(ps - the PHH is at the bottom of that metal pipe)

interesting though - that your hoses are warm....indeed after 20 mins - they should be faily warm to the touch -
as they are flowing with coolant being heated by you block...

Bf
 
Does replacing the HCV require draining all the coolant, or can I expect to just dump what's at the top of the system in those pipes out as I replace it, and then run it again while elevated to bleed out air bubble I'm creating?
 
You must log in or register to reply here.

Share this page

Back
Top Bottom