A/C works but weakens above 90F. Tested, and looking for next steps

[SmoothLC]

Welp, this certainly isn’t helping things:

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Weird that Uncle T puts a filter access door on the 99 evaporator box but then ships that model year with no cabin filters. I don’t think it’s even been opened

I’m gonna vacuum it out and re-test.

Weird yes, but in my case a bonus!

 

[Super77]

What’s the condition of the evaporator fins, are they clean and free from any obstruction?

See my post today. Just cleaned it.

my guess is the fan clutch isnt as strong as it once was, or your condenser and/or evaporator is dirty

Second part proved true.

I may have missed it somewhere, but what are your engine coolant temps during all of this testing?

Is the vehicle just in park while you are testing vent temperatures

How old is your radiator?

Yes, in park during testing, did not measure coolant temps but it's a 1-year old OEM radiator with a recent block flush and the correct coolant. But the vent temps I'm seeing stationary are the same as in motion.

So... re-tested today after cleaning the evaporator and the pressures all were within spec range for the ambient temp: 25-28L / 175-200H / 85 static @1500 RPM. But my lowest recorded vent air temp was ~8 degrees higher (44-45F) than when I tested yesterday under similar conditions but with a dirty evaporator. And, no bubbles in sight glass, which the FSM says is an overfill condition.

Condenser fan is confirmed working and hummed along nicely during this last test.

 

[BonS]

Perhaps one of your blend doors is not fully closing as it should and bleeding hot heater core water into the airstream. Some blend door systems have foam as a final seal and that could have rotted or fallen off. Your evaporator picture showed a lot of straw like material that could have migrated into a blend door seal. (Some versions of the LX470 have a cable driven heater core valve shut-off but the North American version circulates hot water full time through the heater core.)

AI says:

• Servo vs. Foam Failure: This issue is typically caused by one of two things on a vehicle of this age: either the air mix servo motor internal gears have stripped/worn out (preventing it from pulling the door completely shut), or the factory foam insulation tape on the perimeter of the plastic blend door has dry-rotted and blown away, leaving a physical gap for hot air to bypass the door even when the servo closes it completely.

Quick Diagnostic Check
With the vehicle fully warmed up and the A/C running on Max Cold, grab a flashlight and look under the passenger side dash near the center console stack:

• Watch the Servo: Change the temperature on your climate control screen from Max Cold (65°F) to Max Hot (85°F) and back. Watch the plastic linkage arm on the air mix servo.
• Check the Swing: If the servo moves smoothly but stops just short of its mechanical limit, you can sometimes gently push the linkage arm by hand to see if it seats the door further and causes the vent temperatures to instantly drop.

 

[Mike NXP]

Damn i was hoping your dirty evap area was to blame ....Id be curious how this compares to a system known to be working. Sitting in parking on a 90 degree day revving motor and expecting ice cold air could be asking alot of the AC system ...something could be wrong i suppose but im out of ideas otherwise.

 

[David310]

What are your coolant temps? What happens if you open the hood?

 

[RapidRob]

Okay, I'm moving over to the "outside or heated air infiltration" camp.
If you're getting 40ish degree air at the vents then the system is working.
Get it buttoned up and you'll be fine.

 

[Jack90210]

Yep, get in there with a 90-degree sprayer and clean that evap coil out real good, then clean it more when you think you're done

My '07 blows freakishly cold when the coils are 100% clean and unobstructed, and the refrigerant lines have never been opened up.

 

[Super77]

Closing this thread out (for now). On a drive today at 85F ambient and after cleaning the evaporator and installing cabin air filters, I'm getting 45-50F at the center vent, a 35-40 degree differential. That's really what counts, and that's a normally functioning system by most measures.

I'm also putting automotive A/C in the same box as crop circles and missing socks in the laundry: it's a Thing That Exists, but don't ask too many questions - they will just lead to more questions. Example: the air vent temp tested a little lower when idling and stationary than when moving at 40mph

Thanks for all the discussion which led me to learn that:

a) my evaporator box was full of debris,
b) my 99 can be 'upgraded' to have cabin air filters (by simply installing them),
c) I have a condenser cooling fan, which possibly only shipped with rear A/C-equipped trucks in 99.

'Mud is amazing as always.

 

[Patassa]

I installed the air cabin filter retrofit kit today because I cleaned my evaporator only 2-3 years ago and it was already filthy with gunk and dust and leaves again. Taking that cover off and doing that job is a major PITA. I used a combo of evap cleaner, a scrub brush, and when I ran out of evap cleaner just dawn and hot water. Cleaned it 4 times, rinses with hot water in a spray bottle. Pick below of all the gunk that came off the fins.

I just bought the filter cover, don't have the part number handy but it's easy to find. Cut out the shape using my Dremel and dropped two aftermarket carbon filters in there. Also changed that weird little bottom foam gasket that eventually leaks water onto your passenger. Also while I was in there, pulled the fan and of course the blades were all thoroughly coated with oil and dirt. Got that cleaned up with hot water. Worth checking that fan bc there will never be a filter upstream of it.

Blows more air, colder air, and smells great!

 

[Super77]

Did you manage to not mangle the fins on the evaporator? They're made of aluminum foil!

 

[Patassa]

Did you manage to not mangle the fins on the evaporator? They're made of aluminum foil!

I used very soft bristle brush that came in my bicycle cleaning kit. Looks like this. Made to not scratch fancy carbon fiber bikes, did the trick and was long enough to reach the back of the evaporator.