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Re: bypass the heater by pass valve. Posted by pme [Email]  (#1496)  [Profile/Gallery]
(more from pme) on Wed, 3 Sep 2025 05:03:38
In Reply to: bypass the heater by pass valve., Don Wollum, Tue, 2 Sep 2025 16:36:36 Members see ZERO ads on the bulletin boards and get more feature. - Help Keep This Site Online - Signup |
While I understand that you are trying to replicate the function of the bypass valve while eliminating the prone to leak automatic valve, there’s one thing jumping to mind in your post.
I agree that setting something up manually is feasible, once you map out the coolant flow. I also agree that maintaining the dehumidifying properties of the AC year round is important (drying the heated air is very effective for defogging).
Unfortunately what I’m not sure will work well is your idea of the ACC moderating the cool air by boosting the temperature to 76 when the heater bypass is active. I think the airflow through the ACC airbox would preclude that.
The airflow is easy to see when you have things apart to change the cabin filter. You can see the sequence of components.
Exterior air enters the system via the intake in the cowl. It then flows through the Cabin Filter and then across the AC Evaporator (cools and de-humidifies), and then if heat is being called for, the temperature blend doors direct the air across the heater core before it enters the distribution ducts. So, all air passes over the AC Evaporator, and after that only air to be heated passes over the Heater Core.
So, if the criteria are met to activate the AC compressor, air will be cooled, and that’s binary - the compressor is either on or off. The temperature regulation is governed by how much of that air is then diverted across the heater core to mix with the cold air. If the heater core is not receiving heated coolant, there won’t be anything to warm the cooled air.
Ostensibly the automatic valve helps with that by feeding the heater core when even small amounts of heat are called for (versus all or nothing in a manual system).
I think that’s why the solution in the past has been just to bypass the valve completely - allowing coolant to flow into the heater core permanently. Because the temperature regulating flaps in the air box can prevent air from passing over the heater core, AC performance is largely unimpeded even in hot humid climates.
Just my 2c (or maybe dime)
~pme
->Posting last edited on Wed, 3 Sep 2025 05:07:04.
, Wed, 3 Sep 2025 05:03:38 <-- Viewing This Message
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