Heater core overheating, panels are hot!

Hello,

I've searched the internets, this, and many other forums and it's still unclear what is going on with my Mazda 5 2008.
Recently I've been working on wiring additional devices behind the glove compartment.
By the time I was almost finished, I had noticed that the AC core, - two aluminum pipes behind the leg trim panel (the one that you take off when changing the cabin air filter) are overheating, a lot. In fact, they are overheating so much that I think I start smelling some burnt plastic, which is not normal.
I have another Mazda 5 from 2014, which is perfectly fine and I'm it using as a reference model. It's not overheating as much.

Symptoms I've noticed so far:
- There's a quiet intermittent squealing noise from the right side of the vehicle. It was there for a while, and I'm sure it's not a belt.
- Both cold/hot and intake/recycle actuators are working as expected, it's not a hot/cold actuator getting stuck
- I can hear the click and noise of the clutch being engaged, I don't think the clutch is going bad, but perhaps, it is?
- New fresh clean cabin air filter is installed, but the problem is still here
- Airflow resistor is ok (the one right next to the cabin air filter) - I've swapped it with another Mazda5 and it works in the reference car just fine and vice versa.
- When I remove the plastic screw-on cap on the high pressure / low pressure intake, I hear a single short "psst", which means the system is not empty, there's some pressure. This "leak" is "normal", I guess.
- No error codes
- The pipes are only overheating with AC on


So, my only hope is that the AC needs to be serviced / oiled / refilled, perhaps?
Maybe it's clogged?
Any other ideas on what is going on?
 
sounds like air is getting into the coolant system, creating an air pocket in the heater core. If so, this means there's a leak -somewhere- letting air in. First thing I'd try is bleed the coolant. Not difficult to do, look up youtube video.
 
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Thanks for the advice! I just got the system serviced, - the A/C refill man said they put an ounce and a quarter of refrigerant into it, and no leaks, they say.

Now the problem is still there, however, I can clearly hear a growling noise when the A/C is activated.
As in the video here: Sounds of a/c Mazda 5 - 2008 (bad?) & 2014 (not bad)

Does it mean the compressor is going bad?
 
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Are you sure it's the AC Evaporator?

You said "AC core" and that's not a thing.

An AC evaporator and Heater core are usually near each other in the HVAC system. Are you sure you're looking at the right one?
 
Are you sure it's the AC Evaporator?

You said "AC core" and that's not a thing.

An AC evaporator and Heater core are usually near each other in the HVAC system. Are you sure you're looking at the right one?
Good question! I'm not sure if I am naming the thing correctly.
I've attached an image, the part that is overheating is the two lines (pipes) behind the metal bracket.
1661288107132.png
 
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And this made me think: what if this have nothing to do with the AC and the problem is with the heater core / heater system valve or something like that?
I think I'll disassemble the center console and will try to locate the source of overheating.

Right now, if I don't turn on the AC, these two pipes are hot, but they are acceptably hot, I'd say.
When I turn on the AC, they get so hot I'm afraid they'd melt the plastic and cause fire.
 
UPDATE

sounds like air is getting into the coolant system, creating an air pocket in the heater core. If so, this means there's a leak -somewhere- letting air in. First thing I'd try is bleed the coolant. Not difficult to do, look up youtube video.
You're probably right!
I pressure tested the system. The system holds the pressure, like 2 minutes or so, with a slight drop from 20 psi to 16 psi.
Now I can see that the hose is dripping coolant around the thermostat.
This may explain the air in the system.

This particular car, according to mycarfax, had the thermostat and radiator replaced in 2016, which explains the aftermarket hose clamps I see.
I also got the coolant flushed like 1000 miles ago. Could it be that the servicemen overpressurized the system? Or the hose was about to start leaking and this stress just sped up the process?

So, tomorrow I'll do the system burping and will install a new radiator cap, just in case.
Pic related, this is what I found.
1661483108648.png
 
Are you sure it's the AC Evaporator?

You said "AC core" and that's not a thing.

An AC evaporator and Heater core are usually near each other in the HVAC system. Are you sure you're looking at the right one?
You're right, this is not an AC core, this is a heater core!
 
Coolant dye and UV/blacklight. Be prepared for 'other' leaks (notorious engine oil cooler gasket) as the 08 are starting to age.

 
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Yep, found one more potential leak.
What's your opinion about proactively replacing all the hoses with silicone hoses?
Proactive is good if you want to play it safe but I’m more of a “if it ain’t broke, don’t fix it” and “less is more”. However, this hinges on you taking the effort to feel the existing hoses and determine if they are good. If unsure, I’d replace.

FWIW, I felt my coolant hoses were structurally sound and the PCV hose was also good.
 
UPDATE:
tightened up the clamp, no more leaks (so far)
burped the coolant - no significant amounts of air were actually trapped inside
while I was at it I finally noticed that the AC clutch started making weird noises and finally
.... suspension ....
AC almost went out while driving around.

Replaced the AC, the panels are moderately hot now, which is normal.
So, I would say, this case is closed.
 
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