93 Ford Aerostar Air Conditioner Problem

I just traded for a 1993 Ford Aerostar and I'm having a problem with the air conditioner. When the van is idling, the compressor stays on and the air blows cold(very cold) and stays cold. But the minute I start driving
it, the compressor(I think it's the compressor) will kick on and off. The a/c will blow cold for a few seconds, then warm for a few seconds, then cold etc...
Some hoses we're recently replaced on it and in *some* research that I've done I've seen mention of a low pressure switch needing adjustment. I just thought I'd check on here to see if anybody had any advice.
Thanks, Kevin
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Kevin opined in

has it been converted to 134A?
does the suction (big) hose tend to frost while idling?
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I'm not sure if it has been converted or not. Is there an easy way to find out? As you can probably tell,I know very little about all of this.
When you convert it to 134a does the compressor turn off and on continuously? I have another car that I was thinking about having converted but I wouldn't like the cold air, warm air, cold air scenario.
I didn't see any frost on the hose.
Thanks for your response.
Kevin
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sure.
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