Im having a few issue's with my heater,

It dosent seem to be working, in that its not filling up the cabin with hot air!!!

The fan is certainly working, but when i move the lever to "hot" the air stay's nice and cold even after the engine has warmed up,

This might be inter-related, but the Front Window de-mister vent's arent working either, no air is coming through the vents, i checked and made sure there was no blockage's and that the hoses were connected and crawled about under my dash to make sure the lever was actually doing something and it certainly is, anybody got any theories on this?

Does your car have 4sp heater that operates via vacuum hoses?

HKSZ makes a good point, if your system is the vacuum operated one, it may be as simple as a leaky hose or a disconnected one.

If on the other hand it is the lever / cable operated system present in the earlier cars (240's), then I would suggest you check the water check valve on the side of the unit and make sure that it IS being opened. If the lever for the temperature DOES move the valve plunger in and out, then you may have to check if the heater core is plugged or if the hoses upstream of the heater are plugged / kinked.

Post some particulars so that we can help you get this fixed before the REALLY cold weather sets in.

E

I have one from a 1977 and it's markings are slightly different than what is in my 1974 260z,

They are both heater/AC units though, when i have a look at my heater it appears it has three different set's of controls,

1st controls - controls the vents, this appeared to be just pulley opereated, when i slid the vents lever from one side to the other it appeared to go through its full cycle of operation - ie.........the little flaps on the heater/ac unit's side opened and closed (BUT) the air vents for the demister aint getting air!!!

2nd controls - operate the heat, this lever appears to move a lever on the right hand side very close to the engine coolant hoses, this appears to be working,

3rd Controls - is for the heater blower unit itself and as im getting the motor to blow out air, this appears to be working fine,

When i move the "Cold - Hot" lever the plunger is connected and it appears to be moving what it is supposed to be moving, therefore,

"then you may have to check if the heater core is plugged or if the hoses upstream of the heater are plugged / kinked."

The hoses are plugged and there dosent appear to be a kink, but, could i have mixed up the hoses from the engine? could this make a difference?

Dont know if this would help, but i have recently completed an engine conversion, i didnt do the wiring myself, get someone eles to do it for me, the heater now works without turning the key on - it can be turned on all the time - could this have something to do with it?

and yes its a 4-spd heater, but not sure if operates purely via vacum hoses,

I'm doing exactly the same thing at the moment, have the same problems. Though I've found that I was missing a few bits of ducting in the dash. I have a 75 and it has the cable operated controls. I found the heater tap on the right-hand ride (with coolant hoses etc) wasn't really opening that well. I plan to replace it with a spare one that visually, looks like it's in a lot better condition.

Id also recommend removing the heater core, (and all the junk that finds it's way in there) and check for blockages in there. It's also really fun taking it out too :tapemouth

On a side note; is the resistor on the blower housing supposed to help heat the air also?

open bonnet and if there is a white bottle on the rh side with vac hoses then it operates on vac.should be if its got factory air.If there is just one small leak (air) then none of the vent controls will work or any hot water taps.

Start at the first vac hose from the manifold, pull it off and you should hear the air being sucked into the manifold then trace this hose and all connections for cracks and holes.

Tip if you have to join a snapped hose cut the inner from a ink pen, the perfect connector.

Engine side is sweet, no leaks there, and both heater hoses of the engine seemed hot, but it was hard to tell,

when i investigated the hoses in the engine bay one of the hoses was not warm at all, one was quiet hot, so i think the tap is not opening properly,

I think i have found the problem, the vacum hoses that come of the heat control were not connected properly, there are two vacumm hoses that go way up into the the unit that were not connected, the hoses had broken, im thinking this might cure my heater woes!!!

However, half of the vacumm hose has broken of on its connection and it aint much fun getting to it, looks like im in for some serious fun today!!!

I have a 280Z that has been converted to RHD; nearly crashed the thing this weekend in the rain when the car fogged up; Like you guys I found a blower motor that seems to work, and all sorts of mysterious vacuum-operated flaps that flip and flop but no air from demister vents and bugger all at full fan from the centre dash vents - in short , useless. It doesnt help that the car has been ****ed around with so much (from LHD injected to RHD Mikuni)

So I hope you guys can shed some light on how to get it hurling gobs of air about the place.

that is crazy, my 75 280 is doing hte same thing. driving in the cold is not fun now. i almost wreaked mine too. i drive 75 miles every morning in 35 degree weather. so what is the prob.?