97 caravan AC compressor clutch always on

I am not gettting cold air from the AC system. I pressure tested the AC system with engine off. I got 70 PSI on low and 75 PSI on high side.

I started the engine and turned on the AC system. I got 12 to 17 psi on the low side and 130 to 140 psi on the high system. I noticed that the AC clutch on always engaged. ( It does not come on when the AC system is not turned on.) Seems like the system is possible low on 134a. But why should the clutch AC be on if a low pressure side reading?

Should I be checking the AC pressure transducer for faulty readings that could tell the clutch to be on?

This might help.http://www.automotiveforums.com/vbulletin/showthread.php?t=909708. Yes it sounds like the a/c is low on freon.

Thanks.

I'' check the transducer volts and let ya know.

I checked the ac tranducer and getting 1.5V which is normal operating range.

The manual says the the ac temperature evaporator probe also controls the ac compressor cycling. The probe is suppose to shut off the compressor if it gets close to freezing.

So I removed the probe and did a few temperature lab tests to determine ohm readings. Here they are:

temp of ice cube.....15K ohms
hot breath..............6K ohms
open flame.............4 ohms (before the probe broke)

I cant find any specs that tell me the normal resistance of this probe.

Are these readings showing me that the probe is faulty?