Auto Air Conditioning & Heater Repair: A/C cycles cold to ambient, 2003 toyota 4runner, magnetic clutch

Question
QUESTION: Hi Wayne,

I have a 2003 Toyota 4Runner (V-8), and the A/C will blow cold for about 10 seconds, then ambient temperature for about 20 seconds. It keeps cycling like this, even on hot days, long before the car reached it's set temperature. Can you give me some ideas as to what the problem may be? I've added some Freon, but no difference. The compressor clutch will disengage during the ambient air part of the cycle.

Thanks for any help...

ANSWER: Hi Steve,

  Here is the most important question for you...

 Does the AC light begin to flash when the system shuts down? There is a revised ac clutch relay (Check to see if technical service bulletin number EL011-05 has been performed. This bulletin pertains to a revised magnetic clutch relay for this problem).  
 The AC compressor has a 'lock sensor' that ensures compressor RPM matches engine rpm.  should the compressor start to slip because of belt tension or clutch wearing out or defective lock sensor/harness the AC will shut off and the AC light will flash.  I have seen literally dozens of these 4runners with this problem.
 Generally speaking tho a system that blows cool, starts to cycle and then shuts off for 20 seconds only to start up again is low on refrigerant. If you have access to gauges I can help you narrow this down.  I would highly recommend starting with a known good amount of refrigerant.  If you go to a shop just ask them to recover and install the recommended amount of refrigerant.  The system will behave like this until it has the necessary amount of refrigerant to cycle properly.  An 80 percent charge will give you this symptom.

Hope this was helpful,

Wayne


---------- FOLLOW-UP ----------

QUESTION: Thanks for the thorough answer Wayne.

The AC light isn't flashing at all. Could there still be an issue with the clutch relay without the light flashing?

I will get a hold of some gauges soon and see what kind of pressure readings I am getting, although I don't have any idea at the moment how many ounces of refrigerant my system currently has.
I know from the manual, the proper amount of refrigerant is between 22 & 24 ounces.

Would the system behave the same way if it was overcharged, as opposed to 80% charged?

Answer
Steve,

 Yes the system could act like this if it was overcharged as the compressor would be shutting off to protect it from the pressures and temperatures.  One way to identify this without gauges is to carefully touch (carefully!) the liquid line that goes from the compressor to condenser.  If it is super hot to the touch it is over charged.  Pressure is proportional to temperature with refrigerant as if too much gets compressed the pressure nad temp goes through the roof.  That lines should be mildly warm to the touch when it is running properly.

Wayne