Hello,

The heater in my '83 blows cold air on all settings. I have the auto system. I feel the return hose from the heater core in the engine bay and it is cold after running the heat for 10 minutes. I also feel the heater control valve and it is cold. My question is, is there a way to test the heater control valve without taking it out? I don't want to go replacing it if it works fine and just the heater core or another line is plugged. Also, can the core be flushed/unplugged without removing the whole assembly from under the dash?

Thank you!

 

If the coolant lines are cold, then there's no coolant flowing through them. Have you checked the coolant level?

 

The coolant level is perfect. The hose that goes into the firewall from the engine bay (sending hose) is hot, but the hose that comes from under the dash back through the firewall (return hose) is cold.

 

I would think either the core is plugged or the temp control valve isn't working.

 

Is that the same thing as the heater control valve or is it something different? Please excuse my ignorance, I am still actively learning about this vehicle.

 

I had the same issue over the winter, i had no vacuum to my heater control valve so it wouldn't open. check to see if you have coolant running to it then check for vacuum i'd say

 

do a simple test to see if the valve works, remove the passenger side kick panel and airduct, the valve should be up and to the left in the center console, get a vacuum hose, hook it up to the valve and suck on the hose and see if the valve opens.

 

Thank you, that's the kind of answer I was looking for. I will try that today.

 

Good news! I did as mrprofile suggested and heat is pouring through! Although I have to keep sucking on the tube to keep the pressure up. What does that mean? Also, what step do I take now?

 

well... the good news is you know you dont have a plugged heater core, as for what to do now, im not entirely sure, you have the annoyingly complex automatic climate control, normally I would say you need to replace the valve because its not holding vacuum, but im not sure if that is normal or not with that particular valve because it needs a way to vary the amount that the valve is open and it may do that by applying more or less vacuum to the valve.

Heres your next step. make sure you are getting vacuum from the hose normally connected to the valve, turn the heat to max and feel the end of the hose for suction, if there is a lot of vacuum coming from it then I would say the valve needs to be replaced, if there is no vacuum, then it is beyond my knowledge of the system, and you will have to look in the FSM to trouble shoot which thing does what to actuate the heater control valve, Datsun made a pretty detailed one.

Before you go crazy looking up stuff in the book, look at what you can right not, look for torn or hard vacuum hoses, or hoses that aren't connected

 

Vacuum pressure is coming from where it's supposed to, but not a lot of it. Not enough to keep the valve open at least. Another line that goes to an air conditioning part puts a hell of a lot more vacuum pressure. I put my fingers underneath the heater control valve and there is a little bit of coolant on it. I'm leaning towards the heater control valve being bad and just replacing it.

 

yea, you should replace the valve if its leaking, I cants remember which valve is harder to get, the manual or the vacuum one, there has been talks before on the forum before about it, if you look in my history i think may have found a link to buying one cheaper then the 100$ that ebay is selling them for.