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Ryan Schott
Ryan Schott,
Category: Chevy
Satisfied Customers: 83
Experience:  technician at Demarois Buick Gmc
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When AC is at full blast after starting the car, and backing

Customer Question

When AC is at full blast after starting the car, and backing out (foot off break) or stopping, the rpm dip down and up. Sometimes after driving and stopping, car feels like it will cut off'
JA: Have you checked the Freon level? What is the model/year of your Chevy?
Customer: 2006, and no haven't checked Freon level. This stuttering started many years ago and I thought it was a transmission issue when reversing. now it happens more often and only when AC is on fan 4
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: Well I was going to try and maybe use a can of Freon to charge it
JA: Anything else you think the mechanic should know?
Customer: when standing outside the car, something is making a rough sound. maybe the ac compressor?
Submitted: 11 months ago.
Category: Chevy
Expert:  Ryan Schott replied 11 months ago.

it does sound like your compressor is creating too much drag, this is more likely due to a failing compressor. The low freon level could have contributed to it but being low would not create drag in and of itself. Some rpm fluctuation is normal when the a/c is on as the compressor is adding a load to the engine. Can you shoot me your VIN so I can pull up the vehicle build.

Customer: replied 11 months ago.
Thanks. VIN: 1G1ZT51F56F111642. As I mentioned before, it started years ago but only happened occasionally. Car was in a garage consistently from 2007 to about 6 months ago so the only time it would be on full blast was when running errands etc. It was most noticeable then and now when backing up for some reason and stopping at the gate to leave my complex (driving in these situations is more coasting or slowing down with no gas applied). The behavior of the rpms would be 1 sec oscillation from below normal to normal for about 10 secs while moving. In the last month when stopping after driving the rpms get really low like the car is going to cut off and the AC even cuts off and the air is warm for a few seconds and then cools. The last couple of days the AC doesn't seem to get as cold as normal after running for a while. I live in the DFW metroplex and for most of August temps were 100+ so I don't know if that accelerated the condition. I can possibly take a video of the dashboard or compressor while running.
Expert:  Ryan Schott replied 11 months ago.

The lower RPMS in reverse with it on is due to line pressure in the transmission being commanded high, It sounds like it is low on Freon however you will probably want to get it evacuated and vacuumed then remove your orifice tube and inspect it for debris.

Expert:  Ryan Schott replied 11 months ago.

here is the process with pictures. it does require a quick disconnect tool to remove the line where its at.

Removal Procedure

Important: Cap all A/C components immediately to prevent system contamination.

  1. Recover the refrigerant. Refer to Refrigerant Recovery and Recharging.
  2. Remove the surge tank from the surge tank bracket.
  3. Remove the suction hose and liquid line nut from the thermal expansion valve (TXV).
  4. Remove the suction hose and liquid line from the TXV.
  5. Remove the line clip from the dash.

  6. Remove the refrigerant filter from the line.
  7. Remove and discard the sealing washers.
Expert:  Ryan Schott replied 11 months ago.

if you can get it out look for metal in the screen.

Customer: replied 11 months ago.
34;The lower RPMS in reverse with it on is due to line pressure in the transmission being commanded high" The line pressure in the transmission is the AC transmission? I have done some car procedures in the past but am not sure I am comfortable working with the AC system. This is my wife's car so I can't be messing around with it for days or risk screwing it up. So it seems you are stating I have low refrigerant and/or a bad compressor?
Expert:  Ryan Schott replied 11 months ago.

That's what it seems like so looking at that orifice tube will let us know if the compressor is actually failing. If it is you want to fix it soon so you don't have to replace that many parts because when they completely fail it can fill your ac system with a ton of metal that is hard to remove. the line pressure being high in the vehicle transmission adds load combined with the extra load from the ac it exacerbates the problem.

Customer: replied 11 months ago.
I guess I didn't think the car transmission and ac were connected in any way. If I take this somewhere to be checked, what exactly should I ask them to do so I don't get unnecessary services?
Expert:  Ryan Schott replied 11 months ago.

Evacuate the system, and replace the orifice tube(or AC filter as some will call it), it is a very cheap part so you want to replace it when you remove it, but have them inspect it for metal or debris so you can see if you compressor is on the way out.

Expert:  Ryan Schott replied 11 months ago.

If it has metal then replace the compressor and receiver dryer. Then check for leaks once recharged, they can add a florescent dye. If it is low we can surmise it has a small one somewhere.

Customer: replied 11 months ago.
Hmm. So if the orifice tube is not dirty then the compressor is good? Will just low Freon be the cause of my issue?
Expert:  Ryan Schott replied 11 months ago.

That can cause excessive cycling but i suspect if this has been a worsening situation you will find metal there.

Customer: replied 10 months ago.
my wife experienced the issue without the AC being on as a test and it still happened. I do think the AC is putting additional load making the symptom more obvious but there has to be something else like throttle position sensor, MAF, idle control valve that would cause this issue

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