Heater control unit knackered or fixable?

Robotsan

Club Member
The heater in my 280z is working, but it only blows any air when velocity is set to 4, and the temp slider is stuck on cold - won't budge at all.

Anyone know if it's fixable, or should I try and source a replacement unit?
 

Rob Gaskin

Treasurer
Staff member
Site Administrator
The heater in my 280z is working, but it only blows any air when velocity is set to 4, and the temp slider is stuck on cold - won't budge at all.

Anyone know if it's fixable, or should I try and source a replacement unit?
Most things are fixable. The biggest issue is do you need to take it out?

The fan problem may be a resistor burnt out but that's a guess. The temp problem may be a seized water valve. You need to get your head under the dash and investigate the valve.

Awkward jobs.
 

Robotsan

Club Member
Most things are fixable. The biggest issue is do you need to take it out?

The fan problem may be a resistor burnt out but that's a guess. The temp problem may be a seized water valve. You need to get your head under the dash and investigate the valve.

Awkward jobs.

Cheers Rob, yeah it looks like a right arse of a job. Was just thinking if it was a common fault then it might be worth tackling while the console is out. But sounds potentially like a big job!

Will it be detailed in the FSM do you think? I'm guessing if I just follow the connections from the temp control it will lead to the water valve..
 

richiep

Club Member
Its all simple and mechanical. And its not a huge arse to deal with tbh. The heater valve is to be found on the RH side of the heater unit, near the bulkhead under the dash. The actuation for it and the vents is all by steel cable. I'd start with removing the centre of the dash (with the heater controls, etc.) and learning the lay of the land in there. It may also be that the mechanism/slider is stuck and needs WD40/manual intervention to free it. Or the cable is stuck/corroded.

New heater valves are available if the old one has had it.

Get in there and start fiddling!
 

Robotsan

Club Member
Its all simple and mechanical. And its not a huge arse to deal with tbh. The heater valve is to be found on the RH side of the heater unit, near the bulkhead under the dash. The actuation for it and the vents is all by steel cable. I'd start with removing the centre of the dash (with the heater controls, etc.) and learning the lay of the land in there. It may also be that the mechanism/slider is stuck and needs WD40/manual intervention to free it. Or the cable is stuck/corroded.

New heater valves are available if the old one has had it.

Get in there and start fiddling!

Thanks Richie, I'll give it a gan!
 

arcdef

Club Member
Its all simple and mechanical. And its not a huge arse to deal with tbh. The heater valve is to be found on the RH side of the heater unit, near the bulkhead under the dash. The actuation for it and the vents is all by steel cable. I'd start with removing the centre of the dash (with the heater controls, etc.) and learning the lay of the land in there. It may also be that the mechanism/slider is stuck and needs WD40/manual intervention to free it. Or the cable is stuck/corroded.

New heater valves are available if the old one has had it.

Get in there and start fiddling!
On a 280z alot of it could actually be vacuum controlled. Again not a super complicated system but youd want to check the feed line and the lines going to each of the vacuum actuators - when mine failed you could hear a faint hissing as a pipe had cracked. £5 in hose replaced everything though!
 

uk66fastback

Club Member
Yes, I’d lie upside down in the footwell, with light and WD40/spray grease in hand and see what you can move … (you might need some pliers if it’s all seized).
 

toopy

Club Member
Have you drained the coolant? the condition of that should give you an idea as to how gunked up the valve and pipes could be!
 

Robotsan

Club Member
Have you drained the coolant? the condition of that should give you an idea as to how gunked up the valve and pipes could be!

I haven't, but I *think* @SacCyclone said it was all flushed out and done before it headed across the pond.

So could that be why the valve is stuck then? Just stuff stopping it from opening/moving?
 

toopy

Club Member
I haven't, but I *think* @SacCyclone said it was all flushed out and done before it headed across the pond.

So could that be why the valve is stuck then? Just stuff stopping it from opening/moving?
Possibly, it could just be bunged up with crud or it could be a molten rusty mess :oops: or maybe it's just the controls that are seized. Either way your back and neck probably aren't going to thank you!
 

Robotsan

Club Member
Possibly, it could just be bunged up with crud or it could be a molten rusty mess :oops: or maybe it's just the controls that are seized. Either way your back and neck probably aren't going to thank you!

I've suffered plenty recently doing the floors and the headliner so a bit more won't do any harm!
 

Robotsan

Club Member
Had a look for and found the heater valve, but it looks a lot less accessible than on the 240 (judging by your pic above @uk66fastback )

1679390008672.png

Found another pic on Google, taken from above it (see below). Think I'll probably remove the whole dash at some point to give me decent access. Found this very useful looking video from 'merica which looks like it was filmed in 1992, but incredibly, is only 2 years old:

There was a coolant leak into the footwells of my car many years ago, hence the rust in the interior - seems from reading up that the likely culprit is the o-ring inside the valve?


1679390062470.png
 

uk66fastback

Club Member
If you’re taking the dash out then wait until that happens … it’s hard work trying to fix this stuff upside down and working in no space …
 

Robotsan

Club Member
If you’re taking the dash out then wait until that happens … it’s hard work trying to fix this stuff upside down and working in no space …

Oh aye, I'll only do it when I've got a few jobs to wrap up in one. And one of those will probably be replacing the dash!
 

Faster Behr

Club Member
Your car has A/C so it has a manual cable operated valve and a vacuum operated valve adjacent to it. On mine the O ring could be fixed but the diaphragm in the vacuum mechanism had failed rendering it useless. The diaphragm I believe was unobtainium the last time I researched it. .

I replaced the crusty looking hoses with 16mm (5/8”) silicone hose pieces that I matched up online. I’ll grab a photo at the weekend.

You might find this thread useful. https://forums.hybridz.org/topic/53249-heater-control-valve-76-78-280z/page/1/#comments
 

Robotsan

Club Member
Your car has A/C so it has a manual cable operated valve and a vacuum operated valve adjacent to it. On mine the O ring could be fixed but the diaphragm in the vacuum mechanism had failed rendering it useless. The diaphragm I believe was unobtainium the last time I researched it. .

I replaced the crusty looking hoses with 16mm (5/8”) silicone hose pieces that I matched up online. I’ll grab a photo at the weekend.

You might find this thread useful. https://forums.hybridz.org/topic/53249-heater-control-valve-76-78-280z/page/1/#comments

That's incredibly useful, thank you very much. I'll bookmark this for when the time comes!
 
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