Heater and AC discussion.

[Av8ferg]

I wanted to start a discussion about the 280z HVAC.   It’s a bit confusing to me and I need some education to make the proper decisions to move forward.  
 

My car is a stock AC car so it has two HVAC control valves.  One is a vacuum valve for the AC and the other a mechanical valve with a thermostatic sensor for the heater.  This sensor has a coiled copper wire that sits under the heater core and the other end goes to the heater valve.  I’m not sure how all these devices work together.  My reading leads me to believe this system is all that great, not to mention stock components are in the unobtainable category.  
 

First are there modern valve alternatives?  Second, there are Nissan heater valves for a non-ac ZX that would probably work, the question is what do you lose with removal of the thermostatic sensor that’s on an AC car?   Not sure why an AC car has this additional sensor and why it is coiled below the heater core?  If I went with a ZX valve and kept the Vacuum AC valve would I not be able to control temperature?  I really don’t know so I can’t make a decision on the proper way forward.  My contact in WI that rebuilds heater valves has gone silent on me so I’m looking at alternatives until he responds.  
i have a new Dash that arrived from Vintage Dashes next week and when I return from my 10 day work trip I want all my stuff ready to go.  I’m not doing this job twice.  I needed the heater stuff squared away before installing the dash! 
I can’t imagine I’m the only person that has had to deal with this, so I’m hoping there is corporate knowledge out there on suitable alternatives.  I live in the South and heat isn’t a must have but it get cold here.  Got done to 28 last night.  Summers are brutal….AC is a must.  Mid to high 90’s during peak summer with humidity 95+ %.   No AC = No Go.   I’d like to have both work.    There is heater valve off a 70’s Volvo looks promising.  For sale on Amazon for $99 with free returns, only difference is the cable connection is on the opposite side.  Could be an easy mod?  Last pics are of this Volvo valve.
Here are pics of the above discussed components. 

 

 

[Dave WM]

from what I recall when looking the heater valve over, the coil is there to alter the fulcrum on the valve. I presume its supposed to allow more or less throw in the opening of the valve to compensate for how hot the heater core is getting, to try and keep the heat constant for any given manual opening of the valve. If I am right then I doubt its function is critical, and if its broken I presume the fixed fulcrum would not really be that big a deal, just reset the manual opening if the temp is not right after the car warms up. 

As for the AC, it works OK in stock form using R-12. I can not comment on how it works with conversion to other coolants, like R-134a or any of the R-12 replacement gases. 

I do like the OE hitachi compressor, sanden and sanden clones seem to dominate the after market alternatives. I have no exp with them but I do with the OE hitachi SWP123 

Its a beast of a compressor, it has a wet sump for oil, and seems to be very well built. its heavy but I dont care bout that I just want it to work, and work it does, my car has I presume the oe from the looks of it and it works find, does not leak but is noisey. 

I have the stock OE fan motor, while its not a hurricane force blower it does ok. I would caution that if you "upgrade" the motor you consider the amp draw, and if it exceeds the stock motor make some wiring changes to allow for the increase. The stock fuse box is stressed as is (the max setting on the fan is for emergency cooling IIRC per the owner manual).

The biggest limitation seems to be the ductwork when it comes to flowing air, there was a mention somewhere perhaps on this forum about a redesigned diverter on the front vents, dont recall any followup.

All the aftermarket evaps and housing make no use of an fresh air supply from the cowl chimney. That has always bothered me. That and they do not use the levers or the logic of the lever as designed so all the markings are useless to functionality. They are universal HVAC systems and seem should not be considered a drop in replacement.

You can buy brand new oe fitment evaps that use a standard tvx (not the NLA stock tvx). I have one of those purchased as a spare just in case my existing evap every goes bad. I like the way the system works and would suggest you try to preserve it if at all possible.

 

 

 

 

 

[Av8ferg]

Dave thanks for all that info.  I don’t have plans to modify the system unless parts availability come into play.  I have a Hitachi compressor.  I don’t know it’s status,  could be junk….or not.  I guess the issue with a Sanden is getting the lines to fit properly.  I usually try and avoid aftermarket stuff but in some cases technology had progressed making it better but most of the time there are fitment and quality issues.  It’s not a hard and fast rule but something I’ve seen in my previous car repairs.  Buy OE once or aftermarket 2x or more.  

Good news, got a hold of the guy rebuilding my heater and ac valves.  Nice guy and price is reasonable.  He said he’s done hundreds of these rebuilds and will have mine working like new.  Sent them off yesterday and they’ll be ready when my new dash arrives from Vintage Dashes next week.  (Thanks for putting your 6 part video series up on the dash replacement). 

 

Edited January 23, 2022 by Av8ferg

[Dave WM]

I would certainly like to see some completed vintage air or others. For me I would see if i could adapt them to use the existing levers, prob not possible with out a LOT of alterations.

The other issue I would like to see is how far they extend into the passenger foot well.

[Roberts280Z]

Even after buying replacement underdash heater hoses, I decided to forego the heating function.  If it's that cold, I won't be driving it.  So, I'm just capping the heater lines in the engine bay with aluminum rods.  I haven't attacked the A/C yet.  It underwent a R-134 conversion about 15 years ago, but plugged up soon after that.  If you still have all original R-12 components, but can't get R-12, I can tell you that I had reasonable success using Red-Tek in another car.

[SteveJ]

25 minutes ago, Roberts280Z said:

Even after buying replacement underdash heater hoses, I decided to forego the heating function.  If it's that cold, I won't be driving it.  So, I'm just capping the heater lines in the engine bay with aluminum rods.  I haven't attacked the A/C yet.  It underwent a R-134 conversion about 15 years ago, but plugged up soon after that.  If you still have all original R-12 components, but can't get R-12, I can tell you that I had reasonable success using Red-Tek in another car.

I have been caught out in weather conditions in the summer where I needed the defrost function. Don't be too quick to say you won't ever need it.

[Roberts280Z]

That's a good point.  I think all newer cars actually incorporate the A/C into the defrost function because of the dehumidifying effect.  However, I suspect that the Datsun system would have to be modified to allow the chilled/dehumidified air to go through the defrost ducts. 

[mailnome]

Yep. In a modern car if you have it set to defrost, on hot or cold, the AC is running to dry the air.


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[Captain Obvious]

I did some digging on-line to try to find good theory description info about that little capillary tube and didn't come up with anything great. I'm probably just not using the right search words, but I couldn't find anything I'm comfortable linking to here. I found stuff, but nothing good enough to link to.

My read on the design is the capillary tube is filled with "something" (either a liquid or a gas)* and it's job is to provide some regulation of the temperature of the air coming off the heater core.  As the temperature of that coiled tube heats up, the fluid inside expands and will push the little piston out at the far end and that will (depending on the position of the temperature control slider) close down the valve some amount.

Been a while since I looked at it in detail, but memory says that sensor/piston device can only CLOSE the valve. It cannot open it.

Memory also says that sensor/piston has a limited range of effect on how much it is able to close the valve. I think if the slider is moved to full hot, that sensor has no effect. And since the sensor/piston can only close the valve and cannot close it, it has no effect when the lever is on full cold. It only provides some temperature control between the two extremes.

 

* I found sources that say "freon", "ether", "alcohol".

[Captain Obvious]

16 hours ago, Roberts280Z said:

I suspect that the Datsun system would have to be modified to allow the chilled/dehumidified air to go through the defrost ducts. 

Correct. With the original system the only location exit for air-conditioned air is the dash vents. There is no way to get air-conditioned air to blow directly onto the windshield for defrost.

Other complications include... The system (being so much smarter than you are) automatically blocks all water flow to the heater core when you switch it to defrost. So it's not like you could even blow hot air out the defrost vent at the same time you're blowing dehumidified cold air out the dash.

[Av8ferg]

Good info here.  I could forgo the heat but that’s not in my nature.  I have an desire for thing to be done right ( both a curse and blessing).  This is a journey not a destination and part of the journey is educational and testing and challenging yourself to doing it right.  If I had a deadline or this was my main transportation then maybe I’d skip the heat too for awhile.  Why take the journey if you plan to skip steps.  When it’s done…it will be done the best I can personally do.  I’ve never been a half arse type of guy so why start. now.
 
To the R-134 issue.  I’ve been educating myself on this.   I’m getting conflicting information.  Some says R-134 molecules are smaller and require changes in the fittings and condenser or you will be recharging your system, every 24 months or so….I’m kind of calling BS on this,  This sounds whacky to me with my basic understanding of Physics (I did major in Physics for 2 years at UMASS).  I don’t claim to be an expert by any means.  I do understand that there are different pressures required between the two systems to reach similar efficiencies so that my be the issue that the R-12 fittings can’t handle the R-134 systems pressures  and the stock hitachi compressor can’t handle it either well.  Again, fact or fiction?   Either way I need a new condenser because mine is beat up.  So an R-134 designed one from Vintage Air is probably better and WAY cheaper that an OE type R-12 one.   Do I just got Sanden or have my compressor rebuilt?  Seems like if going R-134 then Sanden might be the right way to go. 

[Dave WM]

I think barrier hoses are used with the R-134 re smaller size mole. that being said new hoses are prob in order regardless if you plan to use different condensor and compressor. 

If you want to go with just changes to under the hood, I would go with a PF condenser generic that fits the opening in the core support. You may have to relocate the drier as I think most PF have fittings on the same side. Not sure about this...