I have a 93 SC400 and it has something wrong with the heater. There are no leaks.
It used to get warm as designed but recently it takes like 30+ mins for it to start blowing warm air, well after the car itself is warmed up. What's also weird is that even after it gets warm and starts defrosting windows and such, it will randomly go cold again.
I was told that my heater core could be clogged.

What else could cause this?

If it is a clogged heater core, what are some tricks to fix this without major disassembly? I was told if it was a clogged core there is a way to hook a air hose or even a garden hose to it somehow and basically back-flush it out onto the ground, anyone heard of this?

Any help is very much appreciated as it is freezing here now and driving to work with freezing air blowing to keep the windows defrosted REALLY sucks!

I guess I am more asking about the best way to flush out the core since based on my searches, that sounds like the most likely problem.

heater core is fine.

Um, ok, thx for the input, care to elaborate?

Does the fact that I EVER get heat mean the core is good so I should look at the various sensors and such?

I am having issues with my heat, I did many searches and I have seen suggestions for temporarily bypassing the heater control valve. I would do this to both test the rest of the system and eliminate it as a possible cause to my issue.

I am wondering what the down side of this will be? Will my heat just be on all the time full blast? This would just be temp until I could fix or replace the valve/controller.

On the technical side of things, would I just need a Male/Male hose splice and some hose clamps to do this?

Its to see if that is the problem, and if it is PM aliga or RGW and get another one...

Done lots of searching here and other websites.
93 SC400
Symptoms:
Heater blows cold until I am on the freeway, usually at a fairly high speed then it blows hot. At low speeds or sitting still it blows frigid air.

Possible Issues:
ambient temperature sensor
Cabin Temp Sensor
Heater Control Valve (solonoid etc)


Steps I plan:
Check to see if the armature/cable is even moving when set to high or low heat
Check the Outside Temp Sensor inside front bumper
Check Internal Temp Sensor in dash


What I am looking for is a quick and dirty work around to get heat blowing so I don't freeze out my mom and kid driving to Thanksgiving tomorrow.
If I bypass the heater control valve by splicing the hose will this give me full time heat?
If either sensor is completely unplugged will it give me full time heat?

TY VM in advance for reading and hopefully responding to this!

Merged.

I have a similar scenario. I've isolated that warm air will start coming through over 2000RPM. Whether I'm stopped or moving. I have my Heater Control Valve bypassed, and the heat will only function if it's bypassed. If not bypassed heat will not come out at any RPM. AC and all other HVAC functions work perfectly.