It blows cold air but it turns on and off about every 20 sec. Is that normal and if not what might be wrong?

 

Cycling is normal. I've never paid attention to the time frame, though.

 

Typically if its cycling that much its low on freon. Have it checked.

 

can you just do it yourself using one of those kits from like autozone?

 

You can buy a gauge and check it yourself yes. Get a gauge with numbers and no trigger. The gauges with the trigger tend to go bad quick and they will leak.

 

I put a can of refrigerant in it and the guage showed it shutting off around 25 and coming back on when it it gets up to around 55. I was reading online about a CCOT (cycling clutch orifice tube) system the clutch is supposed to cycle off depending on cooling demand, usually around 21-23 psi depending on car make. The air that is blows if very very cold. The article also said the compressor is supposed to cycle off when the cabin temp cools. This happens when the heat load gets lower and the compressor is able to pull the low side pressure down to the setpoint which is usually between 21 and 23 psi. Then it kicks back on at about 40 psi which happens in a couple of seconds. The whole purpose of this is to keep the system from freezing up the condensation on the evaporator and accumulator. So what should i do? put ore refregerant in it? take it to a professional? or is it ok. i dont think i want it any colder

also i found this..........
General Motors introduced the cycling clutch orifice tube A/C system in the 1977 model year. The unique advantage to having a cycling clutch with a fixed orifice tube was that now, the only moving part on the A/C system would the A/C compressor. The fixed orifice tube, which provides a one size, fixed opening for the flow of refrigerant into the expansion valve had replaced the typical expansion valve or TXV valve that opened and closed to control the refrigerant flow into the evaporator.
The fixed orifice tube means that there is always a flow of refrigerant into the evaporator. In order to control the evaporator pressure and maintain the coldest possible temperature in the evaporator without freezing the condensation, the system was designed to cycle the compressor on and off.
The cycling clutch system meant that the typical normal pressure gauge readings of a properly operating system would have a wider range. Of course, the low side pressures would be at their lowest just before the compressor cycles off while the high side pressures would be at their highest. As soon as the compressor clutch disengages, the high pressures start to drop while the low pressures increase. That happens because the fixed orifice tube is always allowing refrigerant to flow through it, regardless of whether the compressor is on or off. As soon as low pressures began to rise causing a higher temperature in the evaporator, the compressor would cycle back on to pull the pressures and temperature down on the low, once again increasing the pressures on the high side. The cycle continues in a controlled manner that maintains mean or average pressures in the evaporator so that the A/C system can provide maximum cooling performance with the minimum number of moving components.
Understand that the CCOT or fixed orifice tube system is still slightly different than typical cycling clutch systems. In other system designs, expansion valves are still used to control the flow of refrigerant into the evaporator. Those typical expansion valves open and close to monitor refrigerant flow while the compressor cycles on and off to maintain proper evaporator pressures. The orifice tube system utilizes the fixed opening in the orifice tube which maintains a constant flow of refrigerant.

Does our blazers have this ccot? i think it might

also found out that when the blower is on 3 and 4 speed compressor's clutch stays engaged and only when it is on lowwer speeds it cycles

 

My blazer does the same thing. The clutch cycles on and off when the AC is on lower fan settings.Higher settings and it stays on.Max Ac on and it stays on.Not sure on cycle time but 20sec sounds about the same as my blazer.
when you have it on Max A/C does it cycle?It shouldnt that i am aware of could be wrong and someone correct me if i am.
Also the low pressure varies depending on ambient air temp.Usually the can has a table that indicates what it should be at different air temps.
From what i remember 25psi is at low end of the low pressure side.
Cycling is normal for the compressor it prevents it from freezing up.
Not sure how it can stay on in MAX AC and not maybe someone else can explain.
Hopefully this helps.

 

well this morning i tried it. put the empty can of refrigerant with the guage on just to see what it is doing for sure. Today it is much cooler outside and it didnt matter if i had it on max or what fan speed it would cycle. it was blowing very very cold air still. compressor would kick on when the guage read 54 and off when it got down to 26. does that seem normal. i mean it blows cold air and its nots freezing up.

 

Well your gauge is probably a little off but the kick on and kick off pressure are close. On max ac and high fan the system should be able to keep itself running for quite awhile. The fact that the pressure is dropping to 26 after it runs for 20 seconds most likely means it is still low. Its compressing all the gas in the system before the rest of the refridge has a chance to flash from liquid back to gas and be recompressed. Its possible this is due to a partly blocked orfice tube or too much oil though also.

 

I would have to agree with portcqb.
Does the accumulator get cold when the compressor is cycling?
If not that typically means the orifice tube is clogged.
Try throwing another can at it and see if it stays on.
Since your pressure is still low.