Heater issues, cold outside air constantly coming in through center vents. I'm cold...BRRRR!

[JoeCool]

I tried search, and gave up after 10 pages about replacing heater cores, that is not my issue. It is fine.  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?

[HRH]

160 degree thermostat is too cold for winter.  Upgrade to 180-195 unless you drive at WOT all the time, like rally cross or something.  There is a plunger on all the early Datsuns that regulates the cold/hot lever.  Usually what happens is this plunger gets blockage from age and either doesn't work or creeps shut.  Try this.  Put lever all the way to cold, then put to hot.  Find the arm that moves when you do this.  Then, after it's on hot, take a rod of some sort and push the little sticky-out that the lever uses back farther towards hot.  Chances are you'll get it an 1/8" farther than the cable can pull it, and miraculously you'll have heat.

 

They creep shut even after doing this, you'll have to do that every time you shut it off.  Solution is to get a new heater valve.  You can get a generic one at any auto parts store.  The one I have at NAPA is a 660- number, think it's like 1408 or something.  Just 5/8s in and out with a little valve.  Very simple, makes all the difference in the world.

[LenRobertson]

I helped a friend with the heater on his 720 a few weeks ago, but I wasn't paying as much attention as I should have. From what I remember, the valve HRH is talking about is under the dash above the passenger side of the trans tunnel. If you can get your head down on the passenger side floorboard I think you can see the heater hose and valve. It might not be moving as much as it should toward Hot and if you can reach it with pliers you might be able to help it along. On the same side of the heater box may be an opening where you can see the heater flap move back and forth when you move the control lever from heat to defrost. It could be this flap isn't going as far as it needs to to divert all the air toward heat. The 720 I worked on is missing the package tray underneath the glove box so maybe was easier to see than one with the tray. I think there are only 3 or 4 screws holding the tray in if you need to remove it.  If you can't see the valve and flap, you may be able to reach up in there with one hand while running the heater controls with the other. Or use a mirror and flashlight to look in there. I'm thinking if that flap isn't working right it might keep all the fan air from blowing through the heater core.

 

Len

 

 

[bananahamuck]

Have you tried this??

 

 

 we didn't notice the fresh air coming through as it is mostly around town truck,, but we went on long freeway run yesterday and holy crap it was cold.

 

 

:rofl: :rofl:

 

 

 

 

 

 

 

 

 

 

 

 

 

It's on the drivers side up behind the control levers.. you could loosen screw and run baling wire through hole and tie it back if you can't get the lower levers to push/pull it to get it shut. You should be able to use the bend in wire ( open/pinch shut )  for extra adjustment also.

 

 

upper link adjust in picture

 

 

 

[datzenmike]

Yeah a 160 thermostat is so 50s. Cars today and 30 years ago are designed to run just below boiling. 180-190 is fine. The engine will run better, longer and cleaner when warmed up.

There is an air mix door that mixes heated and cold air. If it does not seal properly cold air will dilute the heated air. It's on the pass side and you can get at it by removing that large 4"? flexible black plastic hose between heater and the fan over on the passenger side by the door. The hose is ribbed and will compress to give room to get it off the heater. Inside you'll see a flap door. If you move the horizontal lever from COLD>>>>>>HOT, two things happen. One is the heater valve will move towards full open allowing the maximum amount of hot water to flow through the heater core. Two the air mix door should close completely so that all the air from the fan is forced through the heater core. Locate the black cable that moves these two items. First make sure that the lever is free to move side to side and not stuck. Note that the water valve is free to move. Note that the air mix door is free to move.

To adjust the air mix door set the temp control to COLD. At or near the end of the black cable is a clip that clamps the cable. Lift the clip to release. Push the black cable back towards the heater control lever and push the clip back on to hold it. This will remove any slack and should now fully close the flap door and open the water valve when in the HOT position.

 

Another reason for poor heat transfer to the air is sediment in the heater core. To flush part drain and save you anti freeze. In the engine compartment disconnect the two heater hoses (one on the block under the intake and one to the intake) direst a garden hose in one and flush till the water runs clear. Reverse the hosed and flush in reverse till clear. Repeat until only clear water. Connect and run engine with heat set to HIGH to mix the antifreeze in the core

Still another problem is poor air flow from the fan. Pull the large 4" hose from the fan and look inside. Mice will fill this hose and the fan inlet with hair, leaves, straw you name it to make a winter nest. They can even plug the heater core with straw.
 

Fronm my '74 710 fan...

 

[JoeCool]

Thanks for the info everyone. I am going to tear the system apart the weekend and check it out when I have more time. Heck, I hadn't even thought about clogging, and I have noticed the occasional small leaf blows out of a vent. For now I am using banana's idea and taped them up!

[datzenmike]

If you have lots of air flow then it's not plugged.

 

I think a 185F thermostat will solve everything.

[JoeCool]

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!

[wayno]

A small adjustment, a big win. :)

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!