Keeping cool without A/C - heater core bypass

[oldtamiyaphile]

Most cars seem to have heater cores that constantly circulate coolant -whether cabin heat is on or off.

All that separates that heat from the HVAC system is a thin plastic blend door - and the heater box itself must bleed a fair amount of heat into the cabin. Certainly after an hour or more of driving, this must be adding to in cabin heat soak.

So why not fit a valve to the top hose of the heater? Doesn't have to be anything fancy - a manually operated valve that you turn twice a year would be fine. As a temporary test you could just use some wood blocks and a G clamp.

It would also be a great mod for those of us with ACC, as I'm forever trying to guess the temperature at which it will neither use A/C nor bring in unwanted heat.

I've just disconnected my Proton's heater core which got me thinking about this - unfortunately that means I can't run a test to see how much heat gets through a heater core that's 'off'.

[oil pan 4]

Yeah the heater core stays hot and a little door closes it off from the hvac system.
Imports will use a divert valve most of the time.

[slowmover]

The heater core engine coolant charge dehumidifies the HVAC intake air. That’s almost half the “need” of creating a comfortable environment. Allows for lowered compressor run times.

Where summer heat is such that bypassing the core becomes attractive is evidence that the HFAC system is not up to the task.

Vehicle insulation, window tint, window covers, shaded parking are all parts of the approach that reduces demand.

“Demand” is the problem. Design engineers aren’t stupid. But disablement is really a sign that one is delaying maintenance, repairs & upgrades past informed use.

[Baltothewolf]

The heater core also plays a (albeit small) cooling system efficiency bump too. It's more water which = more mass of water to help cool the vehicle. I definitely wouldn't bypass it unless it blew up. And even then I would have it loop still.

[M_a_t_t]

On the astrosafari forum putting a regular brass ball valve inline is a common practice for people in warm environments.
http://digitalcartography.com/n0eq/astro/Heater-04.jpg

[teoman]

How does it dehumidify the air?

Warmer air will basorb moisture from the surrounding air and have the same relative humidity as its surroundings. But because it is warmer, it has more capacity to hold water. So the water content will increase.

If it is just passing by getting heated then total water content stays the same but the relative humidity (amount of water / capacity to hold water) decreases. When you cool it down to its original temp you are back to square one minus the energy needed to cool it.

Atleast that is my understanding.

[Ecky]

Originally Posted by teoman

How does it dehumidify the air?

Warmer air will basorb moisture from the surrounding air and have the same relative humidity as its surroundings. But because it is warmer, it has more capacity to hold water. So the water content will increase.

If it is just passing by getting heated then total water content stays the same but the relative humidity (amount of water / capacity to hold water) decreases. When you cool it down to its original temp you are back to square one minus the energy needed to cool it.

Atleast that is my understanding.

You're correct.

Pretty sure my Insight does, in fact, have a valve that blocks off water flow to the heatercore. See here:

https://www.g1parts.com/auto-parts/2...ter-valve-scat

[cajunfj40]

My 1997 (for parts) and 2000 (needs those parts) Ford Explorers both have OEM heater core bypass valves in them, vacuum actuated. Not just a block-off - they have all 4 hoses hooked up to the valve, it's a bypass.

They also have a blend door, that is apparently a failure-prone part that's not fun to fix, being well-buried in the dash. Haven't studied the system any closer than that.

A heater core with hot water in it doesn't do de-humidification. Hot air has a lower RH, sure, but still has the same mass of water in it. You need the A/C evaporator core with evaporating refrigerant in it (or ice-water circulating through your heater core) to de-humidify by causing water to condense out on the "colder than dew point" surface it presents, and allowing it to drip off and run out the drain pipe under the car (or on your carpet, if that pipe plugs up).

Incidentally, this is why the windshield defogger position on the HVAC dial in a car generally has the A/C system turned on - you want dry air blowing on the back of the windshield. Hot dry air is faster than cool/cold dry air, but wet air sometimes just fogs it up worse.

[Hersbird]

Our mail trucks get so freaking hot sometimes inside. Aluminum, no firewall or floor insulation, big windows and that damn heater core always circulating coolant. I have kinked and zip stripped the heater hose before on some of them. They actually have a valve in the heater lines that in theory bypasses the heater core when you move the control from hot to cold. The problem is they don't seem to always work on these 30 year old trucks.

[slowmover]

Measure the humidity with & without. Unless you like cold & clammy. The inability to modify the AC vent temp is also eliminated when bypassed.