Heater Blowing Cold Air

[jjnjg]

i have a 1992 sc300,approx.one year ago i started having heater problems.The car would warm up normally but once the car was turned off and then started again it would only blow cold air for 10 to 15 min then warm up again.about a week ago it started to blow cold air only,water is fine,temperature gauge is normal,does anyone know what this could be

[rob321]

i have a 1992 sc300,approx.one year ago i started having heater problems.The car would warm up normally but once the car was turned off and then started again it would only blow cold air for 10 to 15 min then warm up again.about a week ago it started to blow cold air only,water is fine,temperature gauge is normal,does anyone know what this could be

I'd check the water vacuum solenoid valve, which allows coolant to circulate into the heater core. The module is near the firewall in the engine compartment. To test it I reversed the electrical connection in mine and it stayed open all the time. I obtained a replacement Water valve VSV from a salvage yard and it's been working since.

[rob321]

Correction: Forget reversing the electrical connection. To test the Water valve VSV, swap the vacuum lines in the module: run the tube going into the top of the round vacuum valve to the electrical swich and vice versa. This should allow constant vacuum on the valve while the car is running and keep the water constantly circulating into the heater core. This would indicate the valve is functioning but the electrical switch in the module is not. It's been a few years since I did this and I just remembered how I tested it.

[MSRMusic]

Correction: Forget reversing the electrical connection. To test the Water valve VSV, swap the vacuum lines in the module: run the tube going into the top of the round vacuum valve to the electrical swich and vice versa. This should allow constant vacuum on the valve while the car is running and keep the water constantly circulating into the heater core. This would indicate the valve is functioning but the electrical switch in the module is not. It's been a few years since I did this and I just remembered how I tested it.

Hey, Rob321. My sc400 is also having heat problems. Dealer told me it could be a problem with the heater control valve.

My question to you: Is the heater control valve the same thing as the water vacuum solenoid valve?

Here's a picture of mine

http://lh5.ggpht.com/_AcSRZQZTpeU/TPMFRfy4wWI/AAAAAAAAA9w/iaPcFtmUcSE/s800/100_0457.JPG

If this is the part you are talking about, are you saying to take the tube from the top circular area and switch it where?

As much details as possible would be helpful.

and Any help is appreciated.

[rob321]

I believe this is the same thing and is certainly easy to check. Disconnect the shorter vacuum hose from the top of the round vacuum valve (yours in the picture has the asterisk * printed on it) and you may leave this unattached. Remove the other longer vacuum hose (yours printed with the O #) from the connection below the electrical switch and attach this hose to the top of the round valve. When your car is running this will pull vacuum on the valve and, if the round valve is functioning properly, will open coolant circulation into your heater core. There are some good pictures posted in the following link:

http://www.clublexus...trol-valve.html .

[MSRMusic]

I believe this is the same thing and is certainly easy to check. Disconnect the shorter vacuum hose from the top of the round vacuum valve (yours in the picture has the asterisk * printed on it) and you may leave this unattached. Remove the other longer vacuum hose (yours printed with the O #) from the connection below the electrical switch and attach this hose to the top of the round valve. When your car is running this will pull vacuum on the valve and, if the round valve is functioning properly, will open coolant circulation into your heater core. There are some good pictures posted in the following link:

http://www.clublexus...trol-valve.html .

Hey, Rob. THANKS!! for the details and link to the other pics. I was looking for good pics like these for a while. I'll read over this and try it.

Much appreciated!

[kevin4747]

Want to see if I can get advice, it would be appreciated. I have a similar problem in that my heater (92 SC400) blows cold air, but the big concern is the temp gauge rises past level, but then the heat will start and the temp needle will drop right back to normal. This just happened today with my first use of the heat this winter. The gauge reading is alarming, but this SC has been perfectly maintained throughout its life, and has been fine in Florida summers. Going to check coolant level when car is cooled down, but what other parts should I look at?

[rob321]

Want to see if I can get advice, it would be appreciated. I have a similar problem in that my heater (92 SC400) blows cold air, but the big concern is the temp gauge rises past level, but then the heat will start and the temp needle will drop right back to normal. This just happened today with my first use of the heat this winter. The gauge reading is alarming, but this SC has been perfectly maintained throughout its life, and has been fine in Florida summers. Going to check coolant level when car is cooled down, but what other parts should I look at?

Sounds like a thermostat going bad or low coolant level. My 92 SC400 recently had a leak in the coolant reservoir-- the old plastic became cracked. I replaced the reservoir, then a week later the plastic top part of the radiator developed a leak. I replaced the radiator with an all metal one (not sure why sections of the original were made of plastic) and have had no more coolant loss. I'd have a mechanic do a pressure test on your coolant system to make sure it is leak tight. The above posts might help if you are still having heater issues.

[kevin4747]

Thanks a ton. Keep you posted on how I resolve the issue, bringing it to Lexus soon, as I can't find any leaks, coolant level is fine, fan works, love this car and want to keep it perfect.

[sc400InTraining]

Yo my heating was doing the same thing so what I would do in the morning is crank the heat all the way up and have it blowing as much as possible with the vents closed. and when the car was at regular operating temperture I would then open the vents back up and voila! heat. I'm not really sure why this works but it does so I lost intrest in fixing the problem intelligently, hope this helps those on a budget