Air Conditioning Gurus please help...

[Iron Chef]

How much Freon did you install? Did the clutch remain engaged? What were the gauge readings on both sides? Have you checked to see if the heater valve is shutting off the water flow? (feel both heater hoses)

We put in 3 cans of freon (14oz per can).  Readings were 200 on the high side and 20 on the low side which are not correct.  We put a thermometer in the A/C vent and it registered no lower that 120 degrees and when we opened the heater valve it shot up to over 150 then we closed it, so I think the heater valve is working (it's also brand new).  The clutch kept cycling on and off, and I'm not sure if it's supposed to.

[y3chargerrt]

20 on the low side is too low. It needs more freon.

[Iron Chef]

20 on the low side is too low. It needs more freon.

You  may be right, but I think 4 cans is too much.  I suspect there is another problem lurking somewhere...likely something simple.  I hope.

[John_Kunkel]

Even with only 2.6 pounds in the system it should cool below the ambient temperature.

[elacruze]

How much Freon did you install? Did the clutch remain engaged? What were the gauge readings on both sides? Have you checked to see if the heater valve is shutting off the water flow? (feel both heater hoses)

We put in 3 cans of freon (14oz per can).  Readings were 200 on the high side and 20 on the low side which are not correct.  We put a thermometer in the A/C vent and it registered no lower that 120 degrees and when we opened the heater valve it shot up to over 150 then we closed it, so I think the heater valve is working (it's also brand new).  The clutch kept cycling on and off, and I'm not sure if it's supposed to.

Compressor clutch will cycle due to the temperature switch, which acts as a freeze switch. Your cycling could also be due to the low pressure switch-on modern stuff it cuts out about 10psi, could be closer to 20 on some. Your differential is too high-you have a blockage somewhere. I had a faulty expansion valve from Classic Air, right out of the box had numbers about 250/10. Replaced and went to 160/35.
If you didn't replace your filter/drier, you need to. If it's plugged you might see the lower half of it icing up; you shouldn't be able to feel a temperature difference anywhere on the filter. You can use an infrared thermometer as well to indicate difference. You also shouldn't be able to see any icing at the expansion valve, the refrigerant should get 6-12" downstream (into the evaporator) before boiling and cooling. Bypass the heater core altogether to eliminate that with certainty. New parts are no guarantee of function.

[John_Kunkel]

The subject car is a '70 E body and, to my knowledge, there is no switch in the electrical system but the low pressure switch on the dryer. It could have been altered with an evaporator switch.