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Heater issues, cold outside air constantly coming

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JoeCool View Drop Down
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    Posted: 16 Nov 2014 at 5:14pm
This truck has never had what I would call "good heat" since I bought it in 2011. I am used to having heat on "max" and then having to adjust the temp down and cut the fan down, but this thing gets lukewarm at best. And the damn windshield stays fogged unless I leave it on defrost. The first winter I had it it was really awful, until one day I found a hole in the firewall where a rubber grommet had dryrotted, gooked that up with black RTV. Solved that. And I figured out the stupid side vents bring in cold air the first winter, so I shut those off, WTF kind of idiotic design is that?

 

I have warm air blowing in through the defrost vents and floor vents, but no matter which setting I use the damn center vents are bringing in cold outside air! Yesterday morning it was 23 degrees and I froze the whole damn 24 mile drive to work! I gotta fix this! Hell, I just now have gotten it so I can drive the truck at all in the winter, used to be with the old Craptachi carb if it was below freezing the P.O.S. would not crank and if it did it wouldn't stay running. With the new Weber it does good! I can hear it "clunk" when I switch it to recirculate, and the air through the center vents slows down, but it is still coming in. And the owner's manual says to leave it on outside air setting to keep the windows defrosted, NO WAY, that is like driving with a window down... WTF?!

 

Relay and heater core are fine, tested both, and like I said I have warm air, just changed the coolant (50/50 green) and installed a new 160 degree thermostat this summer. Blower motor works, all three fan settings are good, blendor seems to be working as I do hear a clunk when switching it over. I can't shut the middle vents off like I can the two outer ones. This truck has become my daily driver now, so I need the heat working properly. I'm confused, anybody know what is going on?

*1980 Datsun 720 pickup*

"If it falls off, it doesn't matter" Tom Magliozzi of Car Talk

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EzCruiser View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote EzCruiser Quote  Post ReplyReply Direct Link To This Post Posted: 17 Nov 2014 at 12:36am
I would change thermostat to at least a 180ºF or a 190ºF if you'd like to get it hotter.  I can't remember exactly but when I had a 180 in mine, it would run you out of the truck.  I would leave fresh air on, heat and open the side vents to outside air and it made it nice and comfy, usually..
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smooth620 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote smooth620 Quote  Post ReplyReply Direct Link To This Post Posted: 17 Nov 2014 at 5:37am
Be sure the heater core isn't clogged. Swap in an OE thermostat. All L series engines are very efficient when properly heat soaked.
Better to learn from other peoples mistakes than to make them yourself.-Anonymous

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Braden620 Quote  Post ReplyReply Direct Link To This Post Posted: 17 Nov 2014 at 9:54pm
First off you need to understand these trucks aren't a modern vehicle and they never will be.  Moist air is normally removed via the evaporator but since we don't have ac in these trucks the moisture circulates the passenger compartment and increases the more you breathe. These trucks also aren't what you would call airtight. That's something you will just have to deal with and accept it the way it is.  As far as getting heat I would suggest taking a look at the heater core itself and the coolant valve.  Most likely your core is clogged externally with leaves and dirt.  Removal is extremely simple and some hvac coil cleaner (inside and out or the core), hot water and a vacuum to the air box should cure this.  Next look at the coolant valve and its control cable.  Make sure its opening fully when you switch over to the heat setting. Mine came loose once and I had to re attach it @ 70 mph.  The valve is rebuildable and O rings are available at any parts house. Simply cleaning the valve may simply help it's operation. The fresh air vents are just that, for fresh air.  You might complain about them now but you wont in the summer I guarantee it.  The heat should only blow through the floor and defrost vents, if its coming out anywhere else then you have an issue with the control cables and springs and or the foam sealant on the "blend" doors.   Even after all of this when the heater is working 100% it still isn't up to par with modern systems, our blower motors are weak even on high, our trucks aren't well insulated, they leak air, and the heater cores aren't ultra efficient.  That all being said mine warms up to a comfortable temp after 10 or so miles.

Edited by Braden620 - 17 Nov 2014 at 9:58pm
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Rusty View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rusty Quote  Post ReplyReply Direct Link To This Post Posted: 19 Nov 2014 at 1:17am
Every 620 I've owned has had great heat. I kinda read thru everyones post, but take out the heater box unit, check the core, if it flows good. Check all the air flow lines for crap, and I would take all the old foam stripping off and replace.
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JoeCool View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JoeCool Quote  Post ReplyReply Direct Link To This Post Posted: 19 Nov 2014 at 8:56pm
Being "modern" is irrelevant as I am 42 years old and have owned/driven plenty of old vehicles. My 1976 Chevy Monte Carlo had some HOT heat, and the fan was broken, stayed on high. I would literally drive around in the winter with the driver window down to regulate it! I have also ridden  in a 66 Ford truck with a a rust hole in the floorboard that was warmer than this!  But this spring I plan on insulating the firewall, doors, floor, and rear of cab with Dynomat and carpet, or a thick rubber mat. But I  mainly want to do that for soundproofing.


Thanks for the info everyone, I am going to tear it apart this weekend when it is warmer and I have more time.  For now I just covered the vents with duct tape! 

Edited by JoeCool - 19 Nov 2014 at 9:04pm
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JoeCool View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JoeCool Quote  Post ReplyReply Direct Link To This Post Posted: 20 Nov 2014 at 7:27pm
Okay, got off early this afternoon as work was slow, and it was in the 50's this afternoon so I took a look at it. Tightened the cable under the passenger side dash. That fixed it! Drove it around tonight,as  temps dropped down into the 30's, even got it up to 80mph, no more cold outside air coming in the center vents! I kept the heat on high and was sweating, I even unzipped my coat. AWESOME!
*1980 Datsun 720 pickup*

"If it falls off, it doesn't matter" Tom Magliozzi of Car Talk

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EzCruiser View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote EzCruiser Quote  Post ReplyReply Direct Link To This Post Posted: 20 Nov 2014 at 8:42pm
Awesome, glad you fixed it that easily!
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ZacharyProhodsky View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ZacharyProhodsky Quote  Post ReplyReply Direct Link To This Post Posted: 20 Nov 2014 at 9:01pm
Glad you fixed it man!
I had.. well still have a problem where I have to use a screwdriver to
push on the end near the fire wall because it is so sticky and the
knobs on the control don't do anything.
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Rusty View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rusty Quote  Post ReplyReply Direct Link To This Post Posted: 20 Nov 2014 at 10:22pm
Good deal! Love an easy fix.
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