Heater core bypass...incase anyone was interested

[flcruising]

I have the main parts together for a fully automatic heater core bypass system.

If you have replaced your cabin filters or been at the passenger foot area for any reason while the engine was running or not long thereafter, you may have been nearly scorched like myself from a gentle touch of the heater core pipes that are within inches of the a/c evaporator. I've already done the evap temp sensor mod, but am hoping that a greater benefit will be the approach of keeping the hot coolant out of the passenger compartment altogether. Reading on other vehicle forums, this mod can decrease the a/c output by 5* or more - very noticeable. IOW, if it's hot outside and your a/c is blasting, it won't be fighting the heat of the heater core as well.

The basic components are as follows...

• Heater core bypass valve
• Vacuum switching valve (VSV)
• Electronic thermostat

The basic operation is as follows...

The e-thermostat senses ambient air, then at a user adjustable temperature (approx. 80-85* F), engages the VSV, which - via vacuum to the bypass valve - diverts coolant back to the engine without traveling through the heater core. Once ambient temperature drops below the preset point (1* or so hysteresis), the e-thermostat disengages the VSV, which then causes the bypass valve to route the coolant normally through the heater core.​

If the weather and my wife's schedule cooperate this weekend, I'll pickup some vacuum line and antifreeze/coolant. I'd be happy to do a 'How-To' if any are interested.

 

[StealthWyvern]

linkes to said parts and or part #s?

 

[Silentnoise713]

I have the main parts together for a fully automatic heater core bypass system.

If you have replaced your cabin filters or been at the passenger foot area for any reason while the engine was running or not long thereafter, you may have been nearly scorched like myself from a gentle touch of the heater core pipes that are within inches of the a/c evaporator. I've already done the evap temp sensor mod, but am hoping that a greater benefit will be the approach of keeping the hot coolant out of the passenger compartment altogether. Reading on other vehicle forums, this mod can decrease the a/c output by 5* or more - very noticeable. IOW, if it's hot outside and your a/c is blasting, it won't be fighting the heat of the heater core as well.

The basic components are as follows...

• Heater core bypass valve
• Vacuum switching valve (VSV)
• Electronic thermostat

The basic operation is as follows...

The e-thermostat senses ambient air, then at a user adjustable temperature (approx. 80-85* F), engages the VSV, which - via vacuum to the bypass valve - diverts coolant back to the engine without traveling through the heater core. Once ambient temperature drops below the preset point (1* or so hysteresis), the e-thermostat disengages the VSV, which then causes the bypass valve to route the coolant normally through the heater core.​

If the weather and my wife's schedule cooperate this weekend, I'll pickup some vacuum line and antifreeze/coolant. I'd be happy to do a 'How-To' if any are interested.

Yes, please, on the how-to.

I am not all that familiar with HVAC systems but is this what’s causing the fan to blow out HOT air, even though outside air is cool, due to heat saturation? Mazda's HVAC system is my 2nd biggest gripe about the Mz5...

 

[flcruising]

Do you mean with the blower turned OFF and just fresh air coming through the vents on a cool day?

The HV/AC system works acceptably on the highway, but once you slow down and sit in traffic, the air is unacceptably warm. Maybe it's because the radiator fan can't move enough and the heater core is effecting the interior. I don't know, but this will be the last and greatest attempt on my part to help out the system.

 

[Silentnoise713]

No. On a cool day, With the AC off and recirc open, air coming thru the vents are cool. However, if I turn on the fan (recirc on or off) the vents blow our warm air. Always noticeably warmer than outside air, even on lowest temp. Something, upon turning on the air, is manipulating the air making it warmer. I think it is the heater core or heat from the engine bay getting in throught the cabin air vent. The glove box also gets REALLY hot and can melt chocolate (not puddle but soft melt).

 

[skyhawk]

No. On a cool day, With the AC off and recirc open, air coming thru the vents are cool. However, if I turn on the fan (recirc on or off) the vents blow our warm air. Always noticeably warmer than outside air, even on lowest temp. Something, upon turning on the air, is manipulating the air making it warmer. I think it is the heater core or heat from the engine bay getting in throught the cabin air vent. The glove box also gets REALLY hot and can melt chocolate (not puddle but soft melt).

The drawing below shows the heater core is inside the cabin. And of course it is hot, but there is a valve that directs air away or through this heater core.
I think that initially if there was no airflow in the system heat from the heater core of course will linger around. And it is expected to heat up the area of the evaporator too.
The volume of air in this area will initially by hot. Until carried away by moving air into the vehicle and I assume after a while, Temperature of air in the evaporator area will approach that of the moving air (from inside the car - recirc on or from outside - recirc off).

So the bypass valve will work (I see them in many cars when I go to the junkyard). but the problem it is trying to address may not be that much of a problem. The design of the system is such that air does not flow through the heater core if you don't intend for it to do so.



Following is from the 'Technical guide' that used to be floating around the internet.

http://www.mazdas247.com/forum/attachment.php?attachmentid=194017&d=1336921139


Here is a view of the various vanes.

 

[StealthWyvern]

Skyhawk, FYI your link is invalid..

 

[skyhawk]

sorry.. can you try again?

 

[StealthWyvern]

sorry.. can you try again?

no problem. The link still doesn't work but the attachment works!

 

[skyhawk]

test

 

[Silentnoise713]

Thanks Skyhawk. I have to admit that I don't fully understand what is happening with/in the heater core. But If the bypass helps, I'm all for it! It can get hot and uncomfortable near/under the dashboard after diving for a bit in the sun. The black interior does not help either. Hopefully flcruising will get to write up a how-to.

Is the poor design a Mazda thing or do you see/experience this on other cars too? This is the first for me...

 

[jason10phan]

Sounds interesting.

 

[flcruising]

Sorry, no update yet - weather didn't cooperate. About all I've been able to do is locate how/where to mount things. I will provide a link in this post once I have a 'How-To'.

 

[skyhawk]

Thanks Skyhawk. I have to admit that I don't fully understand what is happening with/in the heater core. But If the bypass helps, I'm all for it! It can get hot and uncomfortable near/under the dashboard after diving for a bit in the sun. The black interior does not help either. Hopefully flcruising will get to write up a how-to.

Is the poor design a Mazda thing or do you see/experience this on other cars too? This is the first for me...

I did have those years where I frequent the car 'junk' yards, for parts for my old buick. and see those
'heater core bypass' in some cars Usually japanese cars. And if you think about it
even if the vane is not directing the air through the heater core, the air trapped in the heater core
will have to transfer the heat in it to the passing cool air. Maybe it will work. let us know.

 

[flcruising]

I finalized the installation at dusk yesterday. Took a long-term step-by-step installation approach to this as Mazda utilized almost every nook of the engine compartment, so part placement was challenging. Not much room for additional components.

The wife and I are going on a cruise tomorrow which includes a 5 hour road trip; system performance will be observed then. Based on idling in the driveway, the operation appears to be just like I intended, but an oddity that may need to be worked out, is the electronic thermostat has an observable flicker of the LED indicator when the temperature is hovering around the activation point. The relay does eventually latch, but there is a chatter in the control circuit that can be seen at the bypass valve as well. Hysteresis maybe?

A follow-up will be delayed at least a week because I will be disconnected from the mainland. Yay!