Does your AC compressor cycles on and off every ~20 seconds when idling ( right after cold engine start ) and AC on, full blower speed, around 80 degrees outside? I suspected earlier that something is wrong with my AC system. I think its low on charge but since I dont have any advanced tools, just want to check if its supposed to do it.

 

i am an ase certified mechanic. no, at full speed, full cool, the compressor should stay engaged. it sounds like it is low on refrigerant

 

Non ASE certified here... Never felt the need to purchase a certification...
Its normal operation.
The HP sensor is showing enough pressure on the high side (30PSI)
just before the orifice and the compressor is cycling on and off
just enough to keep the liquid pressure at the orifice correct
for proper cooling.
The AC cycling switch keeps the external temperature of the evaporator
core just above freezing. If the compressor ran continously as the ase
guy above would like to believe, the evaporator would quickly freeze over
from the condensate in the air.
Read all about it for yourself....

 

the ac compressor will not be cycling on and off right after a cold start on an 80 degree day. it will take a while for the evaporator to reach near freezing temps. the bottom line is, if its not cooling as it should, get it checked. be sure to let us know the outcome.

 

Sounds like you need a little refigerant.

 

Thanks everybody. I continued looking into this and it got more interesting... When AC is on FULL BLAST compressor does stay engaged. But both thick lines next to the receiver/drier going to and from evaporator are very cold, all the way to the AC compressor. Should not the line coming from the evaporator be warm?

 

IMHO, if it adequately cools down a car load of people on a hot day in stop-and-go traffic, then it's working properly.

 

I don't notice it much on my mustang but I know my old honda civic cycles the compressor on and off during operation. Regardless of outside temp, a/c setting (full, min), or whether the car has been warmed up yet.