cold under the hood warm air out of the vents the gauge reads 45 psi but my compressure is kicking on and off about every 2 to 3 seconds...........could this be a blend door problem or a pressure switch??? i did jump the wires and the compessure does stay on and the line gets ice cold but still warm air out of vent.......can someone pleas help its hot in az............

 

Yes, it sounds like a blend door problem.

 

Need both sides pressure.

Also, hand-check both the inlet and outlet lines of the evaporator core. If the charge is low, the outlet will be much warmer than the inlet.

Compressor short-cycling is a typical symptom of an under-charge.

A properly operating cycling switch should cause the compressor clutch to engage when the low side pressure rises to around 44-45 psi. The low side pressure should then drop (depending on conditions) and the clutch should stay engaged until the pressure drops to around 22-24 psi. The cycle may then repeat. Total on/off cycle time is highly dependent on your ambient conditions, but generally, you would expect to see minimum on-time of at least 20 seconds at summer temps .

A broken blend door might be indicated if ALL the following conditions are met: Normal compressor cycling, correct charge, evaporator inlet and outlet temps comparable. Additionally, a broken blend door will often flop around, sometimes making noise, but it will definitley cause the vent temps to vary widely when stopping or starting, especially if it it's really flopping around.

Steve

 

True, but if there is limited air flow over the evaporator, then the preesure will drop real fast when the compressor comes on due to no heat load.

 

However, the blend door has no effect on the passsage of air through the evaporator core. It only bypasses or routes air through the heater core as required. All plenum airflow always passes through the evaporator core. Volume of airflow depends on the blower motor function.

His short-cycling is a very normal symptom of low charge, especially since his reading posted is right on the edge of the cycling switch engagement.

Wish we had complete data from the owner. Partial stuff provided by the average owner usually requires a combination of more data and some inference.

Steve

 

if the low side pressure is cycling between 25 and 45 then you migh tbe kicking out due to low gas. if it is 45 psi low side fairly constant and kicking out, then i wounder if someone added gas and it is overcharged. if the high side goes to 450 psi, it will also kick out. in an 90 degee ambient, the compressor will run almost constantly. yo need to have both the high side and low side pressure as the guys said to determine what to do next. dont work on the blend door untill the compressor is running almost constant and doing its job, then check the air temp.