Help me diagnose heater blowing Luke warm.

[Jayboney]

I have a 96 Tahoe that blows lukewarm at best! I can feel the box/heater core under the dash getting hot but only lukewarm is coming out of my vents. I have checked the mode door and I can see when I turn the dial from cold to hot the motor looks to be moving properly. What to check next?

 

[Raspi454]

I have a 96 Tahoe that blows lukewarm at best! I can feel the box/heater core under the dash getting hot but only lukewarm is coming out of my vents. I have checked the mode door and I can see when I turn the dial from cold to hot the motor looks to be moving properly. What to check next?

is it plugged up in there? Sometimes rodents like to make nest in the ductwork

 

[Jayboney]

Good question! Is there an easy way to check? I guess I could pull the blower and check that side.

 

[TechNova]

I had to back flush mine numerous times including removing the block drain and knock sensor.
ALot of rust was plugging the heater core.

 

[Jayboney]

I had to back flush mine numerous times including removing the block drain and knock sensor.
ALot of rust was plugging the heater core.

The heater core itself is getting pretty hot it seems like the air is being restricted in the vents but I will check

 

[Raspi454]

Good question! Is there an easy way to check? I guess I could pull the blower and check that side.

there's screws holding the bottom pan thing on the blower box, i think 7mm or 5/32 but that is for the heater core box. you could probably feed a vacuum hose through your vents and suck out anything that might be in there,
"bottom case cover" for heater core (I think so)

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I think this is the in dash duct work

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[Jayboney]

there's screws holding the bottom pan thing on the blower box, i think 7mm or 5/32 but that is for the heater core box. you could probably feed a vacuum hose through your vents and suck out anything that might be in there,
"bottom case cover" for heater core (I think so)

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I think this is the in dash duct work

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Thanks Raspi454 that's helpful

 

[Jayboney]

Ok, so I took the bottom case off, vacuuming out as much of the vent as I could. I can not see all the way up there but I didn't find anything blocking or stuck. Still no heat. As stated the heater core is very hot but the vent is Luke warm at best. Also I can see the temperature accuator moving but I can't tell if it's moving anything inside even though I hear a noise when I turn the dial. Any other ideas? If the heater core is hot to the touch and there's no heat at the vent I would think my problem would be at the temperature actuator???

 

[someotherguy]

The heater core itself is getting pretty hot it seems like the air is being restricted in the vents but I will check

If the airflow is weak the blockage will be on the fan side of the evaporator core. That's where all the air in the system flows once it hits the fan. Leaves, pine needles, dust (which turns into mud once it hits a cold, wet evaporator when the A/C is on), etc. clog it up over the years. To completely clean it requires total disassembly which is a big job. You can get most of it by pulling the fan out, vacuuming as much as possible in towards the evap from the fan opening, spray with evap core foaming cleaner, hose out thoroughly.

However, even with weak airflow, if your heater core is hot (both hoses - in and out - HOT at the firewall connection), but the air coming out of the vents is NOT hot, you likely do also have a temp control actuator problem or perhaps the door itself not working properly.

Dunno why anyone would recommend cleaning out under the heater core; there's never anything more than a slight amount of dust in that area. Everything gets trapped on the fan side of the evap.

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Richard

 

[Jayboney]

Thanks for info. Fan blower/air is fine it's just the temp. I think it's the door for temp. I can see the actuator move when I turn from hot to cold so it has to be that door which was my worst fear as I don't have the space to pull out the dashI think I'm going to have to find someone local to do the job for me.