04 Freestar A/C problems
 

The A/C output temperature varies depending on engine speed. Very little or no cooling when idleing, much cooler at 2000rpm but not as cool as it used to be. Also the passenger side output is cooler than the driver side.

Low pressure side checks 90psi @ 90 deg. ambient temp.

The compressor clutch appears to be engaged constantly with no stop and start.

If that low pressure reading was taken when the compressor was engaged, the compressor isn't pulling any suction and is possibly in need of replacement.
The reading looks more like a static reading at that temp with the compressor not running /engaged. Could you please clarify that point? Did anyone add refrigerant to the system?

Thanks for the reply hanky,

Ran another check when outside temp was 73 degrees and it was 70 psi on the low side.
The compressor clutch stays engaged constantly while A/C is turned on. There has been no refrigerant added

From what you are describing it appears your compressor is out to lunch.
With the clutch engaged constantly you should get a lower low side reading like 30-40 psi. If the system were overcharged you could get a higher lo side reading , but not 70.