Heater not heating!

[datsun dreamer]

I was hoping someone might have an idea of why its not throwing heat...Fan kicks out air but thats it! I know it's summer but i want to get a head start for winter, last year it was under 20 degress some days in the high desert(hesperia) where i live and i was freezing my ass off driving my 620 to work! Any info. will be greatly appreciated...Thanks,Jason

[datzenmike]

There is a valve on the pass side of the heater down near the front, against firewall, near the carpet. It is actuated by a cable from the heater controls. If the valve is stiff or stuck this cable can become unhooked, so work the heat control and see if it's moving the valve all the way.

 

Other reasons for no/little heat are:

 

vent in heater stuck on fresh air not allowing air through the core.

leaves, lint, bugs, mouse nest in heater box blocking the core.

sediment, rust, scale deposits collected INSIDE the heater core preventing water flow or not conducting heat.

missing thermostat, thermostat stuck open (failed) or incorrect heat range.

[spiffinspudater]

Hahaha, same problem I am at right now! I am getting ready to remove the entire heater core and clean it up, and also replace that $40 valve. I looked it up and it is kinda spendy, but I like new parts. Anyways, we were in the exact same boat, except mine leaked a little.

[datsun dreamer]

thanks guys, Mike very good suggestions im gonna start with the valve and go from there.

[]2eDeYe]

that pesky valve, lol

 

...stupid cable grrr

 

:D

[Pacific coast Datsun]

Jason my 521 heater was doing the same thing, air would come out but not get hot. I cleaned out the hoses that go from the lower water jacket to the heater fitting on the firewall, they were clogged with crappy rusty s**t!! Afte rthat it works fine now.....

[datzenmike]

thanks guys, Mike very good suggestions im gonna start with the valve and go from there.

 

If you remove the hose on the side of the head and the other end down by the lower rad hose and put a garden hose up to one of them, you can watch the shit get flushed out. Put the hose on the other end and reverse flush, and repeat until water runs clear. I did this on my old Bronco and the first flush looked like coffee and cream with a hand full of dead flies in it. Heater worked golden after that, and I needed it, ever seen an Ontario winter?

[OL YELLER]

thanks guys, Mike very good suggestions im gonna start with the valve and go from there.

 

Jason...any luck?..if not, remove the entire heater assembly...have the core checked (most shops will do a pressure test for free)..even if you have to replace the core..they are not that expensive..........I would check both of the hoses..replace those if needed...the valve?..you can check that it is working correctly by manually opening and closing it..sometimes just a little WD 40 will help...Check e-bay for the valve if needed..they are almost always on there.....Rockauto.com is also a great source.....stll got my Phone #?..give me a call if ya need to..

[datsun dreamer]

Hey guys, I'm gonna do a flush this afternoon after i get home from work today(working on saturday's...Oh what fun!LOL),I checked the valves last night and they seemed to be opening and closing fine....so im hoping the flush will be all i have to do.

[datzenmike]

The valves on the 720 are virtually the same or 'close enough' so there's no reason to pay too much for a new one. 720 cores are WAY bigger and won't fit. I have a 720 heater in my 620 and funnel clouds form over the vents when the fan is on high.

[hang_510]

someone on the BB list just did a nice write up on replacing that valve, and cleaning up the entire heater assmembly.

[spiffinspudater]

someone on the BB list just did a nice write up on replacing that valve, and cleaning up the entire heater assmembly.

 

Want to post that here in the How Tos?

[spiffinspudater]

heh, I tore mine out and the pictures speak for themselves.

I wasnt sure why I was always hearing a clickin when I turned it on... I see what it is now. MMM, old tape.

 

I cleaned it out but I know my valve is leaking still so that WILL be replaced.

[datzenmike]

Javin, you should win a prise for that. I've seen eagles nests that were smaller lol!

 

Worked with a guy once who lost his BIC lighter down the defroster vent on the way to work. On the way home that night it blew up from the heat. It didn't catch fire just the butane expanded when the plastic softened and BOOM. Paper clips, bottle caps, dead wasps and crickets, Popsicle sticks and dust everywhere.

[RacnJsn95]

Nice that I didn't have to start a thread this time! I too have been curious why my truck wasn't putting out heat, only cold air. So lucky me, I stumbled across this thread.

 

I pulled off the heater core cover to find this...

 

 

Cleaned that out, shot a bunch of WD40 on the cables, and that valve. The valve wasn't stuck, but it was well on its way, worked it back and forth for a while, got 'er moving nice again. But the cable that opperates the valve is garbage, and doesn't work, as well as the cable that operates that trap door under the heater core, so when those two 620s hit the junkyard this month, I'll be grabbing them for sure. As well as anything else rad.

 

Being the resourceful guy I am, I saw the old manual choke cable the PO installed, and since I have electric choke now, I figured I might as well make use of it. So I re-routed the old choke cable, to opperate that valve. NICE! So all I gotta do if I need the defroster is switch the top defrost lever to "HEAT", and pull the choke cable, and fan switch... WE HAVE HEAT!

[spiffinspudater]

Although most of it seemed to be tree crap, I was trying not to look at it too much. I still cant get all the crap out of the radiator(?) for it. I have tried shooting air through it, running it under water, pounding the thing on the ground (external casing leave clearance) and there is still stuff in it. I can now see through it though.

[datzenmike]

You know if you take the wipers off and remove the cowl? behind the hood and in front of the windshield, you could tape some fly screen over the air intake to the heater box. Or maybe screen over the slots in the cowl.

[spiffinspudater]

I was lucky that I already had all the heater core bypassed so I could completely dissasemble and rebuild. Make getting that crap off the grate easier. Oh yeah, my pipes were clean. Whoever was having rust in theirs should probably check their radiator... that could be a good cause of the clogged tubes.

[laniadude]

I have that problem too...But do your guy's defrost put out heat? mine does..I will clean my heater core and hopfully get some heat. Nice tip on the screen under the cowl!!

[djmoreron]

wow, i think i need to do this too. ive been cleaning a lot of leaves and twigs out of the engine bay lately.... so mine prob looks just the same. i dont get any heat, but it does blow air. good to know and another reason i love this forum. although, socal winter dont nearly get as cold as ANYWHERE north of here. think its gonna be 75 degrees tomorrow :cool:

[laniadude]

How hot is everyone's heater getting?? Mine is about 74 degrees....using a infrared thermometer....is that normal??

[pope_face]

Sounds a bit low... But, the heater in my truck doesn't work either... actually, neither do the blowers. But, the heater in my daily blows HOT. I've never checked it with a thermometer, but it's hot enough to make my hands hurt if I hold them over the vent for too long...

 

Are you getting enough hot water running through the lines? Maybe your lines are clogged somewhere and you're not getting enough flow... I'd check that, or maybe the heater itself is not switching to full heat when you move the lever (or however it's operated).

 

Does anyone know what other heaters could fit? Or where I could track down a decent aftermarket one or so? I think the old-school VW buses used a similar heater, but mounted under the seat... could something like that be rigged up to the vents?

[datzenmike]

Lack of hot air from the heater:

 

1/Does the fan operate at all three speeds?

2/Is the air flow unobstructed by leaves etc. anywhere between the heater core and out through the plenum and grill?

3/Are the cables and doors working? There are flap doors that mix cold and hot air. If it is stuck and not blocking the cold air off, it will dilute the warm air. If the flapper between hot cabin air and defrost is stuck you won't get full defrost air flow when you need it. Has an air vent hose fallen off under the dash?

4/Is the hot water inlet valve hooked up and working? No hot water-no hot air.

5/Are the heater hoses bent or kinked and obstructing water flow?

6/Could the core be blocked with sediment? Unhook the engine ends and flush both ways with a garden hose with the valve in the open position. Keep flushing till the water runs clear.

7/Last... is the engine reaching operating temperatures? Has the thermostat failed in the open position, causing the engine to run cool?

 

You think the 620 heater is weak? Try the 521 heater in an Ontario winter!!! I took the core out and it's the size of the palm of my hand, pathetic! Disparate, I tore the heater assy out of my old Charger and stood it up between the bucket seats and ran longer hoses to it. I duct taped a pair of flex hoses to the roof and ran them forward to blow on the windshield. Good old North Am heaters. By the next year I had a nine inch square by three inch thick finned rad from an air conditioner with a 12 volt fan mounted where the glove box used to be. Hooked the air hoses to the ones in the dash and all was right.

 

Btw. The 720 core is MUCH bigger, but the fan is separate and mounts over by the pass side upper kick panel. This is what I run in my 620 but involves closing off the central inlet air hole in the plenum and cutting a new one for the fan on the upper pass side. I have 4 speeds and can select fresh outside air or recirculate inside cab air through the heater. It works very well but was way too much work.

[Pacific coast Datsun]

Minor problem here. On my 74 620 my hetaer hasnt worked ever since i got the truck back on the road. So i took the cover off the heater & cleaned out alot of leaves & crap & while it was off i looked under to see how the wiring is. I saw a round silver metal part on the side of the heater that has 2 wires coming out if it. Then on the heater itself theres 2 flat connectors w/ no wires connected to them. Under my dash theres a "few" wires not connected to anything & im wondering which ones i need to connect to get it working. I saw the diagrams on http://www.the620.com but the wires under my dash appear to be different colors. Help... i can figure it out w/a bit of advice from you guys :D

[banzai510(hainz)]

want hot air??????

run a 2 core rad with 195 stat

make sure valve is open all the way. esp in the 510s cable binds sometimes. physically move it with your hands and leave it open then just use the vent.

 

if still not hot enough.

Get some cardboard in front of tha radiator!!!!!!!!!!!