Roy Munson

1992 Lexus SC400

Heater problem – Fan blows but no heat. Air conditioning blows cold.

I read extensively through the forums troubleshooting using previous posts

I tried filling up the coolant reservoir but that didn’t work.
The fan sounds like the vacuum shift is working so I don’t think it’s the heater control valve.
How do I check to see if my heater core is still good?
My temp gauge works fine at least it seems to when I look at it via the gauges on my dash.


Are there any other troubleshooting tips out there?

Thanks,

Roy

Lexnorwest

reverse the two vacuum lines on heater control valve... takes 30 seconds max..... if heater works you'll know that's it.

Baby ///M3

Thank you.

I have the same problem on my car. If possible, could you please describe where the two vacuum lines are?

I'd like to give this a shot since none of the methods I've tried worked so far.

Jon

Roy Munson

I switched the hoses and now I have both Heat and AC although I thought I would have one or the other so I'm happy but a bit confused.

Can this reversal I have done in anyway damage any systems on the car?


Hose Location: The hoses lie under the hood near the dash on the passenger side...they are about as big around as a pencil.

Lexnorwest

All you are doing is keeping the HW valve to heater open ..... several posts on here from people that have done this instead of repalcing the valve (around $280 for the part) but..... probably a good idea to reverse hoses when warmer weather arrivews so you AC doesn't have to work quite as hard. Mine has been this way for 3 years, no problems.

Valve is located on upper part of firewall, passenger side. Has 2 small vacuumm hoses, electrical wire and a heater hose attached. If you look through threads on "heater" you find a couple with photos/arrows indicating location.

Baby ///M3

Thanks for the tips.

I went ahead and reversed the two vacuum lines but my A/C is still blowing cold air.

I can now hear, however, some slight "shhh... shh.." noises coming out of the heater control valve (or the device where the vacuum lines are plugged in to).

Is there any other possibility that might've caused my heater to be non operative?

Thanks again.

Jon

Lexnorwest

Most common problem, mentioned in first or second note above, is low coolant..... if you haven't already, top off your coolant reservoir with a 50/50 mixture of distilled water & anti-freeze.

Baby ///M3

That was actually the first thing I did but it didn't work.

Any other possibility that might've caused this problem?

Thanks again.

Jon

dejacky

iTrader: (2)

Baby M3,
how did you fix it? I'm having the exact same problem .

VJ RC51

one zip tie fixes a bad heater control valve

Baby ///M3

Initially, nothing worked for me for a few months.

Toward the end of last year, I thought I must have had the wrong wires to begin with. So I went ahead and played around with the wires on the heater control valve by switching them around. After that, the heater just suddenly came back for me. It's been working flawlessly ever since.

Jon