1999 Burb Front A/C not cold

My rear air blows COLD. Front.. not so much. What should I be looking to replace/test?

Auto or manual AC controls?
First make sure it has a good R-134a charge.

With compressor jumped and running post back you low and high side readings at idle and at 2K.

With a ac recharging gauge set.
Like one of these.
http://www.ackits.com/merchant.mvc?Screen=CTGY&Store_Code=01&Category_Code=RefrigerantGaugeSets


Low side should be close to 30 lbs.
If it is dropping under 25 lbs the switch will cycle or shut off compressor.

Manual controls. Charge is good. Stays in the "green" zone on the Artic Freeze tester/filler from Autoparts store. Goes to the top of the "charged" zone and cycles off then drops to the bottom of the ''Charged" zone then cycles back on. At idle in 95 degree heat the compressor stayed cycled on & running great.
Without the $90 gauge set, does the above info help?

99 Suburban 144,000 mi. 2500 7.4L 4X4 K&N, Headers, 3" Exhaust

Could it be the Temp control door? When did this problem start? Have you done anything that could coincide with the start of this? Can you turn the front temp control to hot and back to cold and feel the difference? Is your Sub a new body style or old body style '99?

Ah, so many ?'s.

We really need some good accurate gauge readings at idle and at 2K RPM.
What is low side lbs reading at idle and at 2K?
What is vent tempt on rear and front air?
Is the low side inlet pipe cold on front air?

Have you added any pure R-134a?
Or any of the stop leak and any oil stuff that comes with the Death Kits?

If it has a good charge the low side should range around 30 LB low side with compressor running.
At Idle it is normal for low side to climb up 5-10 lbs up over 30 lbs.
At 2K or on the road Low side should go back down to 25-30 lb range and cycle on and of some.
At around 25 lbs low side it will cycle off and then at around 45 come back on.

I've got the same issue with my 99 burb. check the recycle switch and door and temp control door for proper operation. If the system is holding freon in the reccommended range/pressure, and the evaporator is iced up or freezing cold then the problem is the temp control door or recycle door. there is no reason other than that for the front to blow warm and the back to blow ice cold.

And if the evap is not cold replace it........

I've got the same issue with my 99 burb. check the recycle switch and door and temp control door for proper operation. If the system is holding freon in the reccommended range/pressure, and the evaporator is iced up or freezing cold then the problem is the temp control door or recycle door. there is no reason other than that for the front to blow warm and the back to blow ice cold.

And if the evap is not cold replace it........


Unless the evaporator is leaking there is no reason to replace it.
MT

Unless the evaporator is leaking there is no reason to replace it.
MT..


Could be clogged!!!

thanks for all the advise!
Where/how do i check the control door for operation and /or check the evapoator for cold/freezing?
There was nothing done to the rig before this started happening.
Thanks again, hopefully this will help someone else too.
I got a set of gauges, will check today hopefully and post the numbers.

Could be yes.
But in the last 45 years of working on AC I never did see a evaporator clogged/stopped up inside.
MT

OK, here are the readings

Low side at idle 32psi.
High side at idle 160 psi

Low side at 2000rpm 18psi to 50psi back and forth
High side 125psi to 160psi back and forth

Where/how do i check the control door for operation.

Sub up to operating temp (15 miles). A/C on. Mode control to dash outlets. Temp control to hot. Do you feel hot air? Temp control to cold. Do you feel cooler air? All of this should happen within 4-5 seconds and is checking the temp control door operation.

Once again, new body style or old body style?

Will check those things. Old body style.
Thanks for the help!

Ok, tested the vent door operation. Turned to hot, it heats right up, turned to max air cold, cools down right away but only cools to 71 degrees front vents but 54 degree rear vents. It is 74 degrees outside air temp.

could the dryer have anything to do with it just curious...

This is the same thing as my 98!

OK, here are the readings

Low side at idle 32psi.
High side at idle 160 psi

Low side at 2000rpm 18psi to 50psi back and forth
High side 125psi to 160psi back and forth


Pressure reading show it may be a little low on R-134a

High side is low and low side at 2K should not be going up and down very fast or compressor should not be turning on and off very fast.

While you have the gauges on it add a can and see what it does.
If you get to much the high side will go way up and low side will climb up.
Add a little at a time and watch gauges.

But as 777stickman said conform the tempt door on front unit is switching all of the way back and forth.

You may have to remove the front temperature actuator the one on front of heater housing and switch it manually.
Set tempt to cold and remove actuator and check for the door being in cold position.
Feel for binding and listen for door to flop over from hot to cold.
If you can get actuator and door in full cold side put actuator back on and unplug actuator and try AC.

You are not alone. I am also having a similar problem. One thing I noticed was my aux fan was not kicking on when I turn on the a/c. I dont have the correct wiring print ( I've been using a chilton's book for up to 96) but I believe the fan should turn on when the a/c is on. My pressures are good( The high should be about twice the ambient temp) I took the lower valance panel off to see the blend door actuator and it appears to be in the full closed position. I haven't had time to go any further. Hopefully if we bang enough of this info around we can figure this out. Yes The fan is good, and I changed the relay. No help. My next step is to get a current witing diagram and go from there.

I just added 3 - 13oz. cans of r-134. Wow, what a difference! Low pressure is still only at 35lb at idle but cold air is a blowen' out the front vents. What I don't get is why the rear vents still blew cold before I added anything, they both feed off the same compressor so......? Oh, well I guess I watch for leaks and enjoy cold air up front for now.
Thanks for all the help.

I just added 3 - 13oz. cans of r-134. Wow, what a difference! Low pressure is still only at 35lb at idle but cold air is a blowen' out the front vents. What I don't get is why the rear vents still blew cold before I added anything, they both feed off the same compressor so......? Oh, well I guess I watch for leaks and enjoy cold air up front for now.
Thanks for all the help.
You are welcome and thanks for posting back how it went.
If it is low on gas one unit will rob the other one of cooling.
Big dog eats the little dog.
MT

It was cold in the rear now its cold up front!

They are now both cold and working properly.