My A/C compressor is clocking on and off and regular cycles every couple of seconds on my '72 vista. I had it recently topped off with coolant. Any thoughts?

 

Could Be Overcharged. Low Pressure Should Be 30-35 High 200-250 but Never Over 300 When Read With Set Of Double Gauges. Have Car Running about 2000 RPMs. Larry

 

I know....I know...

BUUUUT.....coolant goes in the radiator and refrigerant goes in the A/C system.

 

I assume this car has one of those POA eliminator devices on it to cycle the clutch?

 

Nice, refrigerant sound better?

 

I was just ribbin ya man.

 

I agree with rocketowner. Sounds like your compressor is shutting off on high pressure. Check your charge.

 

All well and good, but the '72 doesn't have a high-pressure shut-off switch.

- Eric

 

And it was charged with what? R12 or converted to R134A? If converted, it would only need maybe 75% of the charge R12 requires. It may be overcharged, but if, as MDchanic says, there is no high pressure cut off switch, it would just wail until the cows come home, because they had no auxiliary cooling fans then. I would move spectators away until after it blows.
I would check the pressures. As a rule of thumb, low pressure should be 30-40 lbs and high should be 2.5 times ambient temperature. Sounds more like low charge, a bad ground, or a bad evaporator thermostat.
So tell us some more about yourself

 

It has a safety valve on the back of the compressor - if the pressure gets too high, the safety valve will bleed off excess pressure.

- Eric

 

You're right, Eric. Been so long I forgot about those. Then you watched the whole charge dissipate into the atmosphere. I remember when accepted procedure was to put the discharge hose into a bucket of water and let it rip. Al Gore must have been hiding around the corner watching that.

 

I believe that the manual recommends wrapping a rag around the charging hose of the gauge set, then opening the valves slightly, so that the rag catches the oil spray as the gas is vented.

- Eric

 

It was never aceptable to put a refrigerant hose in water. Any minor amount of water would cause major problems in the system. It cause acid to form.
What it is cycling on is the low pressure switch. Check by jumper the switch and see if the compressor stay's on. If so you have low suction pressure. Could be caused by low refrigerant or plugged orifice tube. You need special tools to repair this correctly. Take it to a shop.

 

Except that the '72 did not come with a low (or high) pressure cycling switch (it did have a superheat switch), it came with a POA (suction throttling) valve.

The OP never posted back to confirm whether his system had been modified, or whether he really has an unusual problem.
We are still waiting.

- Eric

 

My question would be how did the system cool with this scenario of clicking on and off? While the systm may not have a cycling low pressure switch perhaps it has the low pressure safety switch?

 

Joe, the low pressure switch is the "superheat switch." It's the one that's hooked up to a time-delay fuse, and when the pressure drops, it just blows the fuse and stays off.
It can't cycle.

- Eric