Defrost problem again

[Wine Hill]

1998 k1500. I had finished the complete rebuild of my HVAC box due to defrost only blowing hot on driver's side. Was working fine after install and first couple months testing it. Now all of a sudden it doing it again. I replaced all actuators, blower resistor, and has all new heater core and verified all cleaned out. I'm stumped. All vents work accordingly to flow as I want them to. But now the defrost is acting up again.

 

[east302]

Is it blowing hot on the driver side and cold on the passenger or are you only getting air from the driver side of the windshield vents?

The air only mixes at the heater core, so all air going to the defrost is the same temperature. It goes up through the top right opening in the air box. The small one on the upper left is to the side dash defrost vents.

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I don’t have a picture of the duct opening at the dash and don’t remember if it is split from left to right through the grill in the dash. You could probably get a mirror and take a look in it to verify and to see if there’s a blockage.

The duct is supported at the defrost grill by the dash screws. Perhaps some are missing or the screws don’t go through the duct screw tabs, leaving the duct at an angle and blowing some air under the dash instead of through the grill.

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[Wine Hill]

Thank you for the help. I'll double check. It was a heck of a project the first time ,but overall it went good

 

[Wine Hill]

Like I said, was working fine when installed it all together. But now the heavy dew in the mornings, I tried it out. Pretty much the same result from where I started. Yes I'm getting plenty I warm air to the driver's side, but hardly anything to passenger side, and that air has no warmth to it. So it condensates the window on passenger side

 

[Wine Hill]

Ok east302, update. It is blowing the same amount of air, but driver side hot, cold on passenger. Definitely feels like no loss of air flow either way, and don't feel any air movement around or under dash. Everything still feels right and secure. So I'm wondering if the temp blend door and actuator is not working properly. Know if there is any way to calibrate while still mounted in place. Still stumped. Thanks for any help

 

[east302]

The air temperature is adjusted at the heater core, so all air coming into that main damper box is the same temperature. It doesn’t sound like an actuator issue or you’d be seeing inconsistent air temperature at all outlets.

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Not really sure why you’d be seeing hot air on the left side of the defrost windshield outlet and cold on the right side. I’d always assumed it was a single duct (not split) up to the windshield from the main air box. I suppose it implies some sort of air leak in the duct, but it seems like you’d see a decrease in air flow in that case.