No Heat in SC400
11-18-14, 09:02 AM
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No Heat in SC400
1992 Lexus SC400 with 170k.... Ok guys, winter is pretty much here now so I've finally had a reason to test my heater and sure enough I essentially have no heat. I will get some heat after about 20 minutes of the car running (or maybe I'm just adapting to the cold jk). Anyways, I have to wait until the engine temp reaches its normal operating temperature to even get any heat out of it. The heat that comes out is NOT very warm either, it's mostly lukewarm, probably around 70-75 degrees. I start getting this heat about 2 miles from when I get to work (13 mile total drive). So this is more or less useless to me. Also, when I come to a stop at a light, I lose the heat. So, even if my car has reached normal operating temp and I'm getting my sorry excuse for heat, I lose it as soon as I come to a red light. When I take off again it starts to warm up the air again. Any suggestions on what I should do?
11-18-14, 09:07 AM
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Also, I did a search and came up with some hits, but they seemed to mostly deal with replacing fuses for the AC/Heating selector/controller in the dash. So, since mine seems to be operating just fine, that didn't help me much.
I did see something about routing some hosing around a vacuum actuator to receive heat to the heater at all times though. I don't know much about this though.
I did see something about routing some hosing around a vacuum actuator to receive heat to the heater at all times though. I don't know much about this though.
11-18-14, 10:04 AM
#3
Sound like you need to bleed you cooling system, there could be air trapped in you cooling system hence when you come to a stop a air pocket gets moved around. If that doesnt help mught want to check your thermostat. Gl
11-18-14, 04:57 PM
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Also, I did a search and came up with some hits, but they seemed to mostly deal with replacing fuses for the AC/Heating selector/controller in the dash. So, since mine seems to be operating just fine, that didn't help me much.
I did see something about routing some hosing around a vacuum actuator to receive heat to the heater at all times though. I don't know much about this though.
I did see something about routing some hosing around a vacuum actuator to receive heat to the heater at all times though. I don't know much about this though.
https://www.clublexus.com/forums/per...t-working.html
11-19-14, 05:17 AM
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Check your coolant levels first to see if you are full on coolant, no coolant means no heat. My sc300 had the same issue, it turned out the switch for the actuator wasn't turning on, This issue has been known to happen, in fact it already has a write up on how to do it.
https://www.clublexus.com/forums/per...t-working.html
https://www.clublexus.com/forums/per...t-working.html
Sound like you need to bleed you cooling system, there could be air trapped in you cooling system hence when you come to a stop a air pocket gets moved around. If that doesnt help mught want to check your thermostat. Gl
11-19-14, 09:48 AM
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Good point. That's a pretty quick cheap fix, so I'll try that. That'll give me a chance to flush the system too.
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11-21-14, 03:33 PM
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Just got my thermostat in today, gonna run up to the parts store tomorrow and pick up coolant. Fingers crossed that does the trick for me. Where is the heater control valve? Let me know if that fixes it.
11-21-14, 10:03 PM
#11
easy way to test heater control valve is to move the plunger by hand and see if heat comes on in the cabin (may need two people for it) or just hook up a vac hose directly to the plunger vacuum actuator
the way the system works is there is a PWM valve that modulates the vacuum to that plunger, and the more vac it gets the more hot coolant it lets into the heater core in the core.
the way the system works is there is a PWM valve that modulates the vacuum to that plunger, and the more vac it gets the more hot coolant it lets into the heater core in the core.
11-24-14, 08:31 AM
#12
easy way to test heater control valve is to move the plunger by hand and see if heat comes on in the cabin (may need two people for it) or just hook up a vac hose directly to the plunger vacuum actuator
the way the system works is there is a PWM valve that modulates the vacuum to that plunger, and the more vac it gets the more hot coolant it lets into the heater core in the core.
the way the system works is there is a PWM valve that modulates the vacuum to that plunger, and the more vac it gets the more hot coolant it lets into the heater core in the core.
11-28-14, 08:32 PM
#14
An easy way to confirm if the HCV is working is to look at the bottom of the actuator from the passenger fender (at fender level) and look at what the rod and pivot arm are doing. Fully extended is max cooling, fully retracted is max heating. I've got pictures of it here. No heat probably means the actuator isn't pulling the rod in to open up the tumbler in the valve and allow coolant through. My problem was the opposite: it wouldn't extend fully, leaving a small passage for the coolant to pass through and heat up the cold air.
