GAsc300

1993 Sc300

I determined my heater control valve needs replacing.

i saw write up here by O. L. T. Keeper of the light guy on heater control valve replacement part by motorcraft. Using this $20 part as workable replacement for $200 Lexus part.

I just got the motorcraft part today and am wondering how the electric plug connector works. The original heater control valve connects to the coolant lines, has vacuum hoses and connects to an electrical plug.
the replacement part lack a way to receive the plug. Is this electrical plug important to operation? The OLT guy didn’t mention it in his write up. Maybe it’s a sensor and not a switch.

If anyone had feedback before I ripped open the bag with the part I’d love to hear it.

thanks

kolbe

LeX2K

The vacuum switching valve which has a connector on it and the vacuum pod are not separate items you can swap over?

GAsc300

I appreciate the help. The parts im replacing are both the pod and switching valve. But they one piece. On the original broken unit the plug plugs into the switching valve piece. The new piece has no plug receptor. I don’t want to retain half of the old piece since it may be broken. Do you know if that electrical connector controls whether valve is open or closed vs a sensor?

don’t know if that helps

GAsc300

I think I’ve figured out my own answer to dealing with aftermarket heater control valves. Only the oem piece has an eletrical connection hanging off it to plug into car’s switch.

So No matter which cheaper replacement you choose you have to deal with fact that Lexus SC300’s electrical switch doesn’t have a way to connect to the new part(s). this switch controls the function of the heater control valve, so without it the new valve will always be open or always closed. Period.

that probably explains the varying experience of past members who connected one replacement heater control valve or another. They either had constant flow into heater core or no real flow. Since none of the non oem replacements connect to this switch they will be open or closed based on their default design (some start off always open or always closed).

if this is correct then you might as well move the heater control arm lever by hand to being always opened or always closed, based on the season. Nothing in the car can control it without the switch connected. Or just by bypass the faulty heater control valve completely and basically have it always opened and always flowing into heater core.

kolbe

KahnBB6

iTrader: (5)

^^ Basically as you found out you need the HCV Vacuum Switching Valve connection which is controlled by the climate control computer. That VSV acts on the vacuum diaphragm device to move a rod that acts on an arm connected to the actual heater control valve itself.

Going off some earlier research by another CL member I started buying aftermarket heater control valves from Autozone stores one after another which all were VERY close in design to the OEM HCV valve. Only one of them worked in the end... I believe it was the aftermarket Four Seasons #74636 for a Sienna minivan I believe (if I am incorrect the exact notes are in the big O.L.T. HCV thread)... and I was able to use that valve within the original HCV assembly successfully after a little Dremel shaving of some unneeded mounting points and after swapping over the OEM metal arm which preserved the correct travel orientation.

None of the other extremely similar Four Seasons valves worked for one reason or another... usually having to do with the valve arm keyway being oriented 180 degrees opposite from the way the OEM Lexus valve keyway was oriented.

However this aftermarket valve was discontinued only a couple of years after I had success with it. I don't know if another copy under another name has come up for sale on Rockauto or another parts site. I haven't checked.

Nonetheless if the OEM valve is ever discontinued we do have a way to add several HCV alternatives... but we need a way to have the HVAC panel computer control it. That's the real issue. Another future idea might be to use a modern electrical style heater core (usually used in EVs) which doesn't use coolant at all in order to generate heat. Then we would need to put some alligator clips on the connector for the VSV and measure the voltage and behavior that the HVAC computer sends to what would be that VSV and figure out a way to translate it to adjust the function to apply to the new heater core unit. It may be far fetched and ambitious but it's a thought if we as a community are ever forced to consider a totally different alternative to how the conventional system works.

What I have done so far is to keep my old full HCV assembly with the valve, VSV, mounting frame, vacuum diaphragm and all even if the valve itself has failed. I just hang on to it for future experimentation if needed.

GAsc300

Thanks KahnBB6!

I’m sure I read your write up of this too.

If no switch connected to vacuum mechanism, then replacement heater control valve is just a pipe that’s always opened or always mostly closed. Skip the headache and just add a piece of piping with lever on top to open and close flow to core as you wish.

I like to drive my car and didn’t want to wait for more solutions so I bypassed my heater control valve and heater core using existing coolant lines plus a stainless steel barb connector.
I disconnected the line going into my heater control valve and one going out of my heater core … and connected these together with no cutting or new hoses, just a connector.
Burped system and an back on road with no leaks and no overheating so far. No heat but I’ll survive in Georgia for most of year.

I had to bypass my core after messing up the brass? inlet tube when I was flushing it. Did all I could to straighten, seal, and hose clamp but it still leaked. Just leave them old heater cores alone! Those connections to heater core inlet and outlet lines are clamped so tightly.

thanks again for your comments

kolbe

KahnBB6

iTrader: (5)

Glad if any of my earlier contributions also helped! For what it's worth, the go-to place to get a new replica heater core made for our SC300/400's is a small company called The Brass Works. They have made replica OEM brass heater cores for numerous classic cars including the LHD MKIV Supra and LHD MR2. I don't think anyone has contacted them yet to made a jig for an SC300/400 heater core yet but that will be my own plan before long since I have a spare one waiting to send in to them once I begin an inquiry.

As to the HCV unit itself and its control, sure we can easily install a manually operated valve but personally I'd still want to figure out some way to preserve or replicate the climate control computer's intentions with full closed, full open and partially open positions.

For the time being it is still possible to purchase the OEM HCV unit. We just have to come up with a more permanent and repeatable alternative solution in the future once that is no longer an option. And that solution may involve a small Arduino device (or similar) that translates the voltage signals and pulses meant for the VSV into commands that would control an electronic solenoid/actuator set up for the right amount of valve sweep in either direction.

GAsc300

[QUOTE=KahnBB6

Great details Kahn.

For me, Until someone replicates that vacuum electrical connector, there’s no point buying any non-oem heater control valve part. When I read the long multi year history of posts on this thread, this point didn’t come through. It’s not a matter of switching vacuum lines or switching direction of flow through valve or any of the many ideas. Everything unit is gonna make flow to core always open or always closed or always something in between.

I can get my $20 back and return my motorcraft part and I learned a lot from your posts.

cheers!

kolbe

KahnBB6

iTrader: (5)

We all try to contribute and help! Welcome!

I really do think that in time a better solution will be an electrical solenoid controlled HCV that can be fit into that location and have the original climate control signal translated for it will be what we should shoot for.... but until then yeah I'd say the OEM valve is easily the better repair. We have all learned a lot from O.L.T.'s big HCV thread and hopefully we can combine that knowledge and come up with such a fix in the future.

texan_176

iTrader: (5)

I had this solenoid fail in my 99 recently and was able to swap it over without opening the coolant lines. I wish I took photos but here is the gist of it if anyone reads in the future.

Go to a junkyard and just buy the OEM solenoid. I paid $8 for it.

To swap it without making a mess of spilled coolant you take out the 2 10mm bolts that hold the whole assembly in the car. Then you remove the bracket the assembly is attached to in the car by taking out 2 10mm bolts that secure it to the body of the car. That bracket has one more 10mm bolt at the top edge where the car wiring harness attaches to it. Remove the bracket out of the car. Now you have room to rotate the HCV assembly to get to 2 Philips screws on the heater valve. Once removed, you can separate the heater valve from the assembly. Be careful to not drop the plastic bushing that sits between the control arm of the heater valve and the metal control rod of the vacuum actuator. With the valve out of the way, you can get at the 1 Philips screw that hold the solenoid in place.

Reverse the process to put it all back.

It is a 10 minute job. Shame on Toyota for not offering the solenoid as a stand alone part. I would have gladly paid up to around $50 for a new one to know I would not need to mess with it again for a long time.

Tallyhoe

Life saver, I need to do this and was looking at how to tackle this. I have the part just sitting in the trunk while I try to figure out an easier way to do it. Wil follow this.

jwalk956

Would this fix my misfire by any chance

GAsc300

the thread you linked was about heater control valve, which controls the flow of coolant to the heater core. If you mean engine misfire, then no, it shouldn’t relate.