Inadequate Heat

[75gmck25]

I would buy or borrow an infrared thermometer and start checking temps in various locations. Engine side of thermostat housing should get up to 195 or higher. Then check each of the heater hoses to see what temp you get there. Then pull off the hvac housing cover behind the glove compartment and check the heater core temp.

While you have the cover off, check the blend door to see it’s moving full travel and routing all air through the heater core. The cable that determines door travel is easy to adjust at the bracket on top of the plenum.

My truck has the heavy duty heater that came with the A/C option, and it gets so hot that you can’t stand it in the cab unless the heat control slider is at about 20% travel. My truck came from North Dakota, and getting enough heat was never a problem there, regardless of the temp outside. Most Squarebody heaters work very well.

 

[AuroraGirl]

I would buy or borrow an infrared thermometer and start checking temps in various locations. Engine side of thermostat housing should get up to 195 or higher. Then check each of the heater hoses to see what temp you get there. Then pull off the hvac housing cover behind the glove compartment and check the heater core temp.

While you have the cover off, check the blend door to see it’s moving full travel and routing all air through the heater core. The cable that determines door travel is easy to adjust at the bracket on top of the plenum.

My truck has the heavy duty heater that came with the A/C option, and it gets so hot that you can’t stand it in the cab unless the heat control slider is at about 20% travel. My truck came from North Dakota, and getting enough heat was never a problem there, regardless of the temp outside. Most Squarebody heaters work very well.

what made it an HD heater? bigger fan and core?

 

[SirRobyn0]

For what it's worth, these are my thoughts all put together. You need to know if the heater core lines are hot or not or if just one. IR thermometer would certainly help but you don't have to have one. Once the engine is fully warmed up both hoses should be quite hot, possibly to hot to touch, but because it takes time for rubber to absorb heat generally the rule of thumb is they should be roughly as hot as the upper radiator hose.

Flow testing by running water and blowing air through the core isn't necessarily going to show you if it's clogged up or not. BTW, I have seen guys ruin good heater cores by blowing air though them so if you insist on doing that be careful about not pumping 100+ psi of air into it. But even pouring a chemical cleaner directly in the core and back flushing will only help limitedly. Ever wonder why radiator shops use to rod out and / or boil radiators in acid to clean them out? Because a little back flushing and cleaner wasn't enough. Back flushing will get out loose rust and sluggy type build up but it won't get calcification build up out as that is a hard deposit whitish deposit. But we don't know that's your problem. Need to know if the heater hoses are passing heat though the core first.

Normal vent temps should be 120F to 140F, some do deliver more but 120F is considered normal. So if you heater blows 120F and you bump the thermostat from 185 to 195, your likely to see about a 5 - 8F increase in vent temps, so it's unlikely that the cooler fan setting is causing a severe lack of heat, but it could be a contributing to issues.

Let me ask you this does the heat get better or worse if you idle it or sit in traffic, or if you run up a long hill?

You said the heat is "Inadequate", if you happen to have a vent thermometer, or even a meat thermometer stick it in the vent and take it out for a 1/2 hour drive or at least long enough to get the engine fully warmed up for a while and shot us some vent temp figures. See if your running vent temps of 100F it might be that your over sized radiator and early cooling fan settings are the biggest problems, or the core is only mildly clogged but if your only seeing 80F at the vents your fan setting, and large radiator alone could not cause this. While you can do the radiator / heat hose test with your hand if you have to, people are not very good at telling the temperature of blowing air with their skin, very accurately. So if your married go barrow your wife's meat thermometer, for the vent test, I won't tell.

Last it is very uncommon for the hot / cold blend door to have issues like this on these rigs, I don't think I've ever seen it before anyway and we do a fair number of squares at work for some reason.

 

[75gmck25]

RPO C42 is the heavy duty front heater, and it can’t be combined with C60, A/C option, which is why I assume it’s included with the A/C. However, maybe it’s a false assumption and I’m wrong.

I’ve also gone through the diagram for fhe C60 A/C option and it seems really confusing to figure exactly what it includes. It shows two blower motors (there is only one) and two blower motor resistor packs (one for heat and one for A/C; but there is only one) near the blower motor relay. I think it’s probably an either/or case for some items, but I can’t figure out why they are both shown on the same option diagram.

The main problem I’ve found with the blend door is that something fell down the defroster vent and it’s blocking the full travel of the door. That upper vent opening is fairly wide, and I found lots of interesting things when I took my heater plenum apart to clean it out. Pens, pencils and rifle ammunition fit really well down the vent if you leave them on the dash.

 

[AuroraGirl]

RPO C42 is the heavy duty front heater, and it can’t be combined with C60, A/C option, which is why I assume it’s included with the A/C. However, maybe it’s a false assumption and I’m wrong.

I’ve also gone through the diagram for fhe C60 A/C option and it seems really confusing to figure exactly what it includes. It shows two blower motors (there is only one) and two blower motor resistor packs (one for heat and one for A/C; but there is only one) near the blower motor relay. I think it’s probably an either/or case for some items, but I can’t figure out why they are both shown on the same option diagram.

The main problem I’ve found with the blend door is that something fell down the defroster vent and it’s blocking the full travel of the door. That upper vent opening is fairly wide, and I found lots of interesting things when I took my heater plenum apart to clean it out. Pens, pencils and rifle ammunition fit really well down the vent if you leave them on the dash.

yeah there is some 30-06 in my dash defroster vents or wherever from there htey could travel.

 

[AuroraGirl]

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this is a random truck, but I was wondering if that looks like 2 cylinder shapes onthe AC(AC tho... not sure if applicable here) box means one is a circulation heater maybe for the coolant or like another plug in that warms that.... im grasping for straws lol.

 

[AuroraGirl]

nvm it seems to be a vac reservoir

 

[WP29P4A]

The one closest to the firewall is a vacuum reservoir canister, the taller one is the filter/dryer for the air conditioning.

 

[75gmck25]

If the vacuum reservoir is disconnected or the vacuum lines are broken, you won't get the A/C controls to work right for controlling air flow. IIRC, with zero vacuum the vacuum doors will default to a position where the air flow is split between defrost and floor heat. Also, in general the vacuum controls have no effect on the temperature of the air flow, since that is controlled by the cable-operated blend door.

 

[LateOnTheBrakes]

As I mentioned and shared videos the blend doors work fine and are cable actuated.

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[LateOnTheBrakes]

I actually set the first fan to not kick on until 220*F. But I am thinking two 1300 CFM fans are overkill. One fan drops the temp by 25*F in less than a minute.

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[LateOnTheBrakes]

Well, I got around to changing the heater core today. Decent heat when the truck is idling for a long time. It will stay at 206*F for a long time before it gets any hotter so that must be where the thermostat opens. But as soon as I start moving it starts cooling down. I have to idle for like 15 minutes to get the electric fans to kick on.

Maybe I need to do the old diesel trick where I block off a portion of my radiator with cardboard to see if I can keep some heat in the thing.

 

[AuroraGirl]

Well, I got around to changing the heater core today. Decent heat when the truck is idling for a long time. It will stay at 206*F for a long time before it gets any hotter so that must be where the thermostat opens. But as soon as I start moving it starts cooling down. I have to idle for like 15 minutes to get the electric fans to kick on.

Maybe I need to do the old diesel trick where I block off a portion of my radiator with cardboard to see if I can keep some heat in the thing.

not a bad thought, just think how long it takes while not moving, now blow cold air at road speed over it, great for cooling things that get hot. also good at cooling things not hot enough yet lol

 

[Blackbeard44]

how did the blend doors look? My LS swapped K20 with a 180° thermostat has good hot air all the time from 120° on up, I have a big aluminum 4 core radiator, I would really take a good look at all the ducting to the vent, make sure blend doors are sealing up, and make sure any holes in the firewall are sealed up. It should be kicking some good heat

 

[LateOnTheBrakes]

I posted some videos of the blend doors earlier in the thread. They actuate as they are supposed to but it's missing all the foam and soft parts though.