New compressor cycles off and on

ACGIRL on Sat March 24, 2012 7:24 PM

Year: 2000
Make: Jeep
Model: Grand Cherokee
Engine Size: 4.7 V8
Refrigerant Type: R134A
Ambient Temp: 54F
Pressure Low: 30
Pressure High: 115

I went to school last year to learn AC for my job,but my experience troubleshooting systems isnt that great.I installed a new Denso compressor,all new lines,new reciever dryer,and switches.I evacuated the system properly,and charged the system to specification using a digital scale,24oz is what the system takes.The system called for pag 100 6oz,and thats correct.Im trying to figure out why my compressor cycles off and on every 6 seconds,the temperature out of the vents is 44-46 degrees,so im a little confused.Should the compressor cycle off and on like this.I hope i didnt mess it up.Im a single mom of 3 boys and cant afford to take it to a shop.Also i do residential AC for 1 year,not automotive.When i asked the guys in Autozone for advice they basically laughed at me,and said take it to a mechanic.I saved up for these parts and want to get the most out of them,thanks so much.

PS the original issue was leak in the metal band at the suction hose.

Cussboy on Sat March 24, 2012 7:30 PM

I'd say wait a month or two until temperatures increase. 54F is not that warm; if your high pressure reading was higher, I'd say that the system is just shutting itslef off. However, I doubt that you can get a decent reading if the compressor cycles so quickly, I think it's likely low on refrigerant, and shutting itself off to protect itself.

My guess is that even at 54F, the high pressure side should read 180 or more. There are books that list pressure v. ambient temperatures.

ACGIRL on Sat March 24, 2012 7:43 PM

Thanks for replying.It is is pretty cool outside,but the digital scale from work said 24oz went in,.The zone control on my ac goes to a low setting of 55,is it possible because of the 55 degree temp outside that its kicking the compressor off on temp?

Dougflas on Sun March 25, 2012 7:16 AM

Just think for a minute. If your residential AC was operating at an anbient of 54*, your head pressure would be extremely low. When AC systems must operate at that low of an ambient (server rooms) they use fan cycling controls to turn off the condenser fan to build up the head pressures. This inturn, will raise the suction pressure so the evap coils won't freeze.

Same principle on your vehicle. Low ambient=low head. Low head= low suction. Low suction = low evap temp. Evap thermistor is shutting down power to compressor.

Try this.... turn on heat in vehicle and get it hot inside. Then block part of radiator with cardboard. Turn on AC. It should run longer.

As mentioned, 54* is out of the operating temp of your vehicle AC system.

ACGIRL on Sun March 25, 2012 2:52 PM

Thank you so much for Answering,i understand exactly what your saying,it makes sense.I realize also that i can screw lines to condensors and
evaporators,but troubleshooting these systems is a whole different area of knowledge.I hope to get there someday,as this field really interests me.

I will get the Jeep hot and block the radiator with cardboard to raise the pressures,Thanks

ACGIRL on Mon March 26, 2012 1:36 PM

You guys were so right,it stayed on longer when i covered the radiator grille area,and got the cabin hot.It never cycled off,and was ice cold.Thank you'z for all your help.

kapilamuni on Sat March 31, 2012 8:55 AM

Quote
Originally posted by: ACGIRL
You guys were so right,it stayed on longer when i covered the radiator grille area,and got the cabin hot.It never cycled off,and was ice cold.Thank you'z for all your help.

my salute for Dougflas
http://www.autoacforum.com/i/expressions/cool1.gif