wavering pressure reading

[umina]

Tried to find my original post and update its status, but could find it :o(
Anyways, found the AC low pressure port on my '01, and hooked up pressure gauge. Started car and turned on AC to MAX with fan on high. Compressor cycles every 4 or 5 seconds. When it kicks in, the pressure climbs to 45PSI, and then the compressor turns off and pressure drops back to 25PSI. Then 5 seconds pass and it does it again, on and off and on and off. Its getting hot here in idaho, and the AC gets cooler than outside, but just barely. Its definitely working, because on vents alone, the air is hotter and humid. So am I just low on refridgerant, would this cause the compressor to cycle whenever its turned on?

When I've tested pressure on other cars, the pressure seems to remain constant somewhere between 25 and 35PSI with the AC on MAX and fan on high, never seen it bounce like this, but then again, never checked on a vehicle that was actually low (just my wrong suspicions that the AC should be colder than it should but it was really fine). I figure if the system would not hold pressure, then I would get a zero reading with the car turned off and the pressure guage on, but I get right around 100PSI with car off, or with just the AC off and car running. I'm probably going to try throwing a can of R134a in on Monday or Tuesday and just assume the pressure is too low and the compressor is continually cycling just to get cold (the metal lines coming from the Dryer canister get cold under the hood, so its definitely doing something, just not enough....)

[umina]

Well I put a full can into the system tonight, took like 20 minutes, but it took it all. The AC doesn't seem to cycle as much, and I get 41 degree temps at the registers inside the car, is this a good temp? The compressor still seems to kick on and off every 20 seconds or so. Its only 70 here, so I don't think it should be having to work so hard to keep pressure. I drove around for an hour or so with the air on just to circulate the new stuff in the system. I think I may need half a can more or so......