99 K2500 suburban a/c problems

derekbell2605

New member
Having some issues with the a/c in my Burban. Back blows colder than front low reading is 50psi and high side is around 125
On an 85 degree day. I've cleaned the evaporator coil up front and added some refrigerant but the gauges didn't move and my temp up front didn't change. A mechanic told me that dual a/c was tricky anyone have some ideas on what could be wrong and what I should do about it.


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rayra

Expedition Leader
If the back is blowing cold and the dehydrator tank (big alum cylinder near the firewall / high pressure port) is cold too, but you get warm air up front, I'd start looking at the air blend door and its actuator / controls. The AC could be fine, you're just getting heater / hot air mixed into the front vents. The actuator motor on the blend door axis might be kaput. It's a $30 part but you'll have to take apart a lot of the dash to get to it.

eta corollary diagnostic, get vehicle to operating temp, turn temp controls to max heat, is the air hot or lukewarm?
 

Flyboat

Observer
I'm about to drop the dash on my 96 to see whats going on. I suspect I have broken doors or doors with no sealing surfaces left.
 

derekbell2605

New member
The blend door actuator is on the bottom of the hvac box isn't it. I've tried the heat diagnostic and it's really hot so I thought I had ruled that out. My line is cold but I have not checked the dryer to see if it is cold I'll check that tonight.


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rayra

Expedition Leader
yeah on the bottom and hidden by that shroud. There's three screws on the shroud IIRC and the one at the far let end near the center console was a real hassle to get to. 7mm iirc, needed a small 1/4" drive ratchet to get at it.

Sometimes the actuators can be 'overdriven' and get out of the proper movement range. You'd still get hot but no cold, that way. From what I've read it seems to happen more often when the temp range is set to max cold or max hot. See it mentioned often in dual-zone system problems in 2003+

You can 'reset' the guts of the actuator, take care to note its gear position when you open the actuator clamshell. One trick is to fire things up and set the temp mix to middle, before shutting down and digging the thing out. Then when you open the actuator you should find the guts in the middle of its range of motion. If it's near one end that was likely the trouble. You can just move to mid and reassemble. Providing the actuator isn't burned out.


There's several of these things in there, heat / defrost, temp blend, left / right zone. The one for the defroster is a real bastard to get to. Deep in the dash guts.


there's a lot of how-to YouTube vids about it.
 
Last edited:

derekbell2605

New member
Checked the dryer cold as ice clamped heater hoses checked temp unclamped hoses same temp at vents. One thing is the compressor never cycles off when the a/c is on don't know if that means anything.


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cyclic

Adventurer
On my 99 Tahoe, the front doesn't cool very well if the Freon is low. The back will be dang near ice with the front just barely cool. Top it off with a can of 134 and it should do much better.
 

Flyboat

Observer
I did replace my upper distribution box. It was a dig to get to it, but the increased velocity of the a/c discharge was worth it. It's pretty cool in all but stopped traffic in the absolute hottest part of the day. I need to re insulate my accumlator, the original fell apart. I may still add a little aux fan to the front to blow on the evaporator or condenser, I get those confused all the time. The part behind the grill. ;)
 

rayra

Expedition Leader
... I may still add a little aux fan to the front to blow on the evaporator or condenser, I get those confused all the time. The part behind the grill. ;)
Radiators cool things. Cooling gasses condense.

/Johnny Mnemonic
 

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