AC Compressor trouble

[Raynman]

My A/C compressor is giving me trouble. Here are the symptoms: Compressor
will engage approx. 5-7 seconds after engine start...but disengages after about 5-7 seconds.Never engages after that. Pressure on low side reads in the red on recharge kit gauge.Looks like above 70 lbs. I changed WOT Relay with blower relay, and no change.I shorted terminals an lps and hps, and compressor did not engage. This is factory air on a 1999 3.0 flex fuel. I have had great AC until this happened suddenly. I did change Coolant temp sender before AC started acting up...any relation to AC system? Any help would be great!!!

 

[LearjetMinako]

Sounds like a low charge of free-on. Try turning the A/C on & off by the climate control knob. It should try to kick-in each time you turn it on.

 

[shadetree]

If you shorted the terminals on the lps, the compressor should start regardless. The compressor is controlled by a relay. Check to see that it is good. With the lps switch jumped, check for voltage at the compressor. If it has voltage, the coil on the compressor may be toast, or a wiring problem. I'm assuming you did check the fuses.:shady

 

[Raynman]

ac compressor continued....

I tried switching relays and got no change. I checked all fuses inside the cab....all were good. So short the lps, and check voltage at the compressor??
Check both wires in the connector .....what should voltage be??

 

[LearjetMinako]

The a/c clutch connector is either on or off. So it should be at least 12V or better when on.

 

[Raynman]

voltage...ac compressor

attached vom to compressor connector....started truck voltage was 14 v for about 7 seconds then zero.....something is shutting the compressor down....
If the freon is low...would the low pressure side read above 70-75 psi?? I bought a can of freon with a gauge on it ..so I'll try to charge it, and see what happens

 

[Raynman]

still not working...

Tried to add freon, could not...pressure was too great...I think the freon is good, just need to get compressor clutch to engage and stay engaged!!!
Checked voltage at lps, and showed 13 v So where am I losing voltage to the compressor???? what to check next???

 

[shadetree]

When the system is off, the pressures will equalize. If the compressor is not staying on long enough to pull the low side down, you are not getting a good reading on pressure.

Electrical circuit is from power on switch, to lps switch, to hps switch, to wot relay, to compressor. The wot relay is monitored by the powertrain control module. You could have problems in any of these areas.shady

 

[Raynman]

so should i short out the lps AND the hps at the same time to bypass them, and see if the compressor runs constantly?