Heater core bypass

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Jdge439

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So, I spent a fortune trying to get the ac working well in my 95 Yukon. Condenser, dryer, compressor, new lines and flushed the evaporator... yeah, didn't wanna pull it. Anyway, the air kept getting hot when accelerating. Thought it was restriction, or anything.

This truck has a part my 95 Silverado doesn't.. a heater bypass valve. Turns out, the vacuum was falling during acceleration, causing the valve to open again.

I hate dealing with vacuum when electronics can be used ( I like my systems independent, ac dependent on egr valve is nonsense to me). I found a electronic bypas kit and was curious if any you guyses had had any experience with something like this.
More importantly, what did do to wire the thing in without using the knob.

I'd like to be able to have it work as if nothing was changed, no extra switches on my dash or anything like that.

Thanks

Jdge


https://www.oldairproducts.com/product/50-1555-electric-bypass-heater-valve-kit-
 

east302

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On my 98 (and I assume the same for your 95) the solenoid on the firewall is energized when the temperature dial is set to “max”. That then allows the vacuum to change the heater valve position. I don’t remember it having much going to it (12V and ground) so maybe you could use that?

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east302

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It’s supposed to energize when the temperature dial is set to the max detent, but it could be your control panel is flaking out with it somehow. I had one where the panel wasn’t sending the 12V to the solenoid, but the controls otherwise worked. I suppose the reverse could happen as well.

On the bottom of the heater valve, there’s a plunger that moves up and down to position the valve. That’s probably the easiest way to see if it is functioning correctly besides checking for voltage at the solenoid connection.


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Jdge439

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Yeah, I've got that zip tied up right now too keep it cold. Our thoughts were it was losing vacuum when accelerating. That's why it's operating fine at low speeds, in the driveway, etc. I'll get a multimeter and test, but since I can 100 percent reproduce the problem by going up hill or accelerating fast, I assumed that's probably correct
 

east302

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Are the vacuum lines new? Should be a hard line from the PCV tee to the solenoid and one soft line from the solenoid to the water valve.

My 98 truck doesn’t have the valve but my Tahoe does. Neither are spectacular in the a/c department (and the functioning water valve only makes a marginal difference) but an open water valve shouldn’t make enough of a difference to cause hot air to come from the vents. I’d wonder if your temperature actuator or the damper isn’t functioning correctly, intermittently allowing the damper to open air flow across the heater core.

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Refrigerant pressures are good?

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Jdge439

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Yeah, everything's fine. From what I understand, the blender door, that would be vacuum controlled is not there, I just have the coolant shutoff instead. When that bypass is open, it's like the heat is on... cuz it is.

When I close the bypass, used a zip tie... works like a charm, condensation forming on exterior of windows charm.. when it opens.. remember that level of Mario where the sun tried to kill you?

So, I know exactly what the issue is, it's just, what's the longest term solution.
 

Jdge439

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To test, If you have that setup, turn on ac and unplug the vacuum line to the bypass, you should then feel extremely hot air.

These 95s are odd but I love them
 

east302

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Hmm, I would’ve sworn you’d have a damper to modulate air flow over the heater core. So there’s no electric damper actuator behind and to the right of the ashtray?

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The water valve on mine is either open or closed, there’s no modulation.


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Jdge439

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Yes, just looked, that's there, and the slide gear you can see or whatever you wanna call it can't move, tries and can't. So I have both a heater by pass and a blend door, and the door is stuck center so I get heat in winter and ac in summer when bypass works... looks like a pain to replace to
 
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