Heater core and A/C controls

I have a 2002 Blazer with manual A/C controls (no cycling compressor). I take it that this system manages temp by mixing an all on evaporator output with heater core output via the temp control/blend door. Do I have this right? I recently bypassed my leaking heating core and it appears that this leaves me with an all out AC output with fan only control.

George

I have a 2002 Blazer with manual A/C controls (no cycling compressor). I take it that this system manages temp by mixing an all on evaporator output with heater core output via the temp control/blend door. Do I have this right? I recently bypassed my leaking heating core and it appears that this leaves me with an all out AC output with fan only control.

George

The bend door should still work mixing outsie/inside air tempt to ac tempt.
Does the blend door move when switching warm to cold on tempt controls?

I should have added that I always leave my system on recirculating. Other than the hot coolant in the air flow when the heater core was still hooked up, the system was working well. The temp control gave a good range of cabin temp.

Two questions:

A) What does the blend door, blend?

B) How does the temp knob control temp?

Thanks,

George

I should have added that I always leave my system on recirculating. Other than the hot coolant in the air flow when the heater core was still hooked up, the system was working well. The temp control gave a good range of cabin temp.

Two questions:

A) What does the blend door, blend?

B) How does the temp knob control temp?

Thanks,

George


The blend door/blend door actuator mixes hot and cold per the tempt contor setting.

With the heater core plugged it is not going to mix much hot with cold because you will not have any hot to mix with cold.
You need to.

Fix your heater core and system should go back to normal.

No heater core hooked up or bypassed you can not expet it to put out heat.
:lol2::lol::nono::grinno:

As in upper post check blend door/actuator for moving from hot to cold and cold to hot as you move tempt control.

Let us know what it is doing.

1) How do I check the actuator/blend door movement with temp control movement? Is the blend door buried in the dash/vent structure or can I see its movement/position without disassembly?

2) It appears that I may have more than one problem. How is recirculating vs fresh air intake controlled? Is there another "door"? How do I check its movement/position? I usually use recirculate (max AC) but I suspect that recently the system is stuck on fresh air intake or at least that's what my hay fever thinks.

Thanks,

George

1) How do I check the actuator/blend door movement with temp control movement? Is the blend door buried in the dash/vent structure or can I see its movement/position without disassembly?

2) It appears that I may have more than one problem. How is recirculating vs fresh air intake controlled? Is there another "door"? How do I check its movement/position? I usually use recirculate (max AC) but I suspect that recently the system is stuck on fresh air intake or at least that's what my hay fever thinks.

Thanks,

George

Actuators can be checked for movement by moving you controls.
And yes fresh air and recirculater and temp mix and floor/dash /defrost are on diferent vcume controled actuators.

Always confirm good vacumn to heater controls before testing.
To get tempt mix to work you will need to replace the heater control.

For what actuators are where and on replacing the heater core.
Get some good repair info like a factory service manual or a All data DIY online subcsription.
When you are replacing heater core test and check all actuators and dooors as you go.
Replacing heater core can run 8-12 hrs labor.
First time longer so figure good 2 days.
Take your time and do it rigt first time will save on having to do it 2 times.
Good luck and let us know how it goes.

So before dash disassembly, verification for operation of the three actuators is hearing them through the dash?

So before dash disassembly, verification for operation of the three actuators is hearing them through the dash?

Yes that is a good start.
Do not forget some good repair info on heater core rrepacement.
That dash and removing ac/heater box is a bear cat.
Ac controls should switch air and tempt and outside air flow and fan control and ac on and off.
But with heater core plugged you will not get much hot heat.
Always check for good engine vacumn to controls.
When you pull lower dash panels you/glove box you should be able to see.
And pull ac control pane and check for good vacumn to it and switching.
With lower panels off and glove box out and heater controls pulled out of dash some watch the actuators and check vacumn lines and watch the end of actuators and doors for good movement.

And when ac heater and heater core is out you can inspect and check all actuators and actuators doors.

Let us know how it goes.

Sounds like a heater core replacement is a big job, thanks for your advice so far.

Can the position of any of these doors be verified with a boroscope through the vents or an inspection hole drilled in any of the cases?

Also, I see a "service access cover" in the Mitchell diagrams. Where is that cover and what does it allow access to?

Sounds like a heater core replacement is a big job, thanks for your advice so far.

Can the position of any of these doors be verified with a boroscope through the vents or an inspection hole drilled in any of the cases?

Also, I see a "service access cover" in the Mitchell diagrams. Where is that cover and what does it allow access to?

You are welcome.
Just watch actuator for full swing in and out and then check vent doors when you are replacing heater core.

It is your ac/heater but.
Why would you want to drill holes in it and ac evaporator like a wood pecker does and aso destroy vent doors and heater case and wind up with no ac and wet feed from holes in drain housing on ac?:nono::nono::nono::nono:

Trying to diagnose before getting into this big job to avoid unnecessary work or strain on precious resources (my transportation, time, and money). Same reason as exploring knees via scopes or hearts with catheters to avoid/confirm major surgery or taking the heater core out of the circuit and pressurizing it independently to confirm leaking.

I can live without the heater core for months or longer so no immediate need to go in but now I also suspect a recirculating door issue which I can't live with (asthma and allergies in the family/Florida/Ragweed). I have used boroscopes through small inconsequential holes to confirm or fix all types of problems in houses, sewers, engines, boats, HVAC's, etc.

Anyone have any pictures of this HVAC (dis)assembly or experience with where the doors are located so I can at least try to confirm the recirculating door functionality. The Mitchel diagram appears to be functional and not necessarily literal (physically) but shows it "near" the interior and exterior intakes. Can I see it with a scope through say the interior intake and if so, which one is it?

The vacuum suggestion is a good one, I will follow up on that one this weekend. The door movement has gotten sluggish in the past year and I can only get minimal activity after the engine is shut off suggesting that the vacuum may be compromised. Is vacuum evenly distributed throughout the truck systems or can there be an HVAC vacuum/actuator issue that is isolated?

Thanks.

Do I understand this correctly?

The various doors (such as recirculating) in the HVAC module box have a preset position due to spring tension and the doors are moved into another position against that spring tension by vacuum and/or electrical actuators driven by the dash controls.

If that is correct what are the resting or non-powered positions of the recirculating, mode, defrost and temp/blend doors. In other words, if there were no vacuum in the line for that actuator, what would be the door position?

Lastly, is there any way to inspect the position of the recirculating door without dash dissassembly?

Thanks.

Do I understand this correctly?

The various doors (such as recirculating) in the HVAC module box have a preset position due to spring tension and the doors are moved into another position against that spring tension by vacuum and/or electrical actuators driven by the dash controls.

If that is correct what are the resting or non-powered positions of the recirculating, mode, defrost and temp/blend doors. In other words, if there were no vacuum in the line for that actuator, what would be the door position?

Lastly, is there any way to inspect the position of the recirculating door without dash dissassembly?

Thanks.

Why are you trying to study and work and worry yourself to death:sarcasmsign:

Chek air flow by looking and listening and feel.
Then watch and check door positions as you tear dash out and disambled.
You can see and check
Just get yourself some good repair info nd start on the heater core rplacement.

You stated.
The various doors (such as recirculating) in the HVAC module box have a preset position due to spring tension and the doors are moved into another position against that spring tension by vacuum and/or electrical actuators driven by the dash controls.
But not so so.
Electronic actuators door have no spring loading.
Double vacumn actuators have no spring loading.
Also some single actuators may or not have acording to vent door setup.
You might a well get in ther and have a look and check while you are replacing heater core.
Good luck and let us know how it goes.