Chevrolet Repair: burb a/c, change pitch, rear heat

Question
The a/s on my 2001 suburban blows cold in the front but not in the rear, The shop fixed the a/c about 6 months ago at the cost of 1300.00 but cant get the rear air to blow cold.They told me they cant figure it out, and to take it to someone who can.

Answer
Hi Shane,

Well, I don't know what you had done for $1300, but it seems to me for that money, they should have gotten you going.  Anyway, I have some suggestions.  I don't know what you had done, or if it worked prior to going there.  So my ideas will be from all angles.  

You have a system in the rear similar to the front.  

It has a rear heater core and I assume a rear evaporator.  

If the R134 cannot get to the evaporator, you will have no cooling.  This could happen because of a pinched hose, plugged hose, bent metal line, plugged orafice tube, bad evaporator, and many of the same reasons that would apply to the front.  

Another possibility is a problem with the blend door.  This door determines hot or cold air flow.  If it is vacuum operated, it may have failed.  It could also be cable operated (I doubt it) and be a bad cable.  May also be electric door and could have failed for an electrical reason.  

Still another angle is the rear heat control center, if you have one.  If it has control of the system, it may override your front control system.  Front should have control over rear control, but may have a problem here.  

To diagnose:  Switch between heat and cool in the rear.  See if the ducts blow different temperatures.  

If not, listen closely for what sounds like the door switching.  You will hear the blower change pitch, may hear the door insulation rubbing as it changes position.  If you hear nothing, listen for air hiss.  If you hear none, it may be an electrical door.  Check for a fuse for that.  

If the temperatures change from hot to warm, then you most likely have no flow to/or from the rear evaproator.  I don't believe that system uses different accumulators.  Make sure that is cold.  That is the silver 'can'.  Should be cool at all times.  If not, you are low on R134.  Check the lines for issues; both to and from the rear.  You return to the front of the truck, radiator area (condensor).  

Hope this helps.

C J S