The A/C system in my 81 928 now seems to be working properly based on my manifold gauges, new EV, new Dryer, new HCV, etc but I'd like it to be a bit cooler for the upcoming Frenzy trip, so I'm trying to eliminate the heat soak that happens when parked. I have wire tied the new HCV closed, but am wondering if I also need a block of or cut off valve for the outlet line.

My question is even though coolant flow is cut off from entering the heater core now, will hot coolant from the system still heat the core when parked from the outlet hose even though it can't flow because the Inlwt hose is blocked?

If so, can I install a manual cut off valve here in the outlet line or should I replace the vacuum HCV with a manual shut off that I close for the summer and open for the winter, or both?

Thanks.


Tied shut HCV

Does this hose need a manual cut off valve too?

 

Pete, I would ziptie the HCV and plug the vacuum line and call it day,
once the engine is hot and the car has sat with a hot engine,
expect the firewall heat to take a few mins of travel to see a reduction in heat before the full potential of AC is felt.
NOTE roll down the windows with the AC on full, for max heat extraction.

NOTE I would suggest that you replace the wire clamp with a band type on your short hose.

Remember the HCV short hose is the weak part of the cooling system,
the reason for this is because the short hose has a lot of flexing to do during its operation.
every time the engine speed changes the short hose flexes

The hose flexing at that small clamp area will fail sooner than a band clamp type.
as the clamp forces are more concentrated to a bending movement.
Also have a spare short hose in the car .

NOTE it also appears that your fuel lines have been replaced,
but the clamps are not the best fuel injection clamps,
I would also swap those out and possibly replace the hoses.
add on some hose insulating sheathing to reject the heat from the manifolds.

 

All you neeed to do is disconnect the actuator arm- it pops off very easily. you then postion the arm manually- the disc in the valve will stay where you put it as it is spring loaded to push the disc against the seat.

You can also disconnect the vacuum line and block it off to stop the actuator arm from stroking.

In my case I have no need for the heater here so I drained down the heater matrix and removed the heater connections altogether- joining the heater hose sections to forn the circuit. If you leaave the heater circuit connected I would suggest you open the heater valve once a week for a few minutes to circulate coolant through the matrix thus ensuring the coolant does not stagnate.

You can also tie the valve disc in the closed position if you like.

 

9k, so sounds like I don't need to add a cut off valve for the heater core retrun line.

Stan, yes, I'm slowly working my way through some of the older lines in the car. As you observed, though those fuel lines aren't original, they also don't look especially fresh.

The short HCV hose is new. I actually prefer these dual wire clamps to the regular band clamps as with regular hose clamps, the adjustment slots cut into the rubber when you get them tight.

If the HCV is wire tied closed, why remove and cap the vaccum line? Does it matter if that line pulls vacuum while it's already in that position?

 

Saves putting a load on the actuator when the ac is running. Not a huge deal.

 

If you really want to make it cold, replace the factory condenser fan with a modern SPAL one. I used a 16 inch one, model #30102048

It gets attached directly to the condenser and will move more air with a lower amp draw.

As an added side benefit, the engine runs cooler too.

I did this in my 81 and the AC was frigid on a summer day in a black on black 928. Probably the easiest and most cost effective cooling upgrade you can make.