cfahey

Hello! First time poster.

I'll start by saying electrical is not my forte -- in fact, I'm a complete dummy when it comes it. My air conditioner puts out cool air ok, but it's only engaged intermittently. I start the car up, turn the A/C on, the RPM drops ~150 RPM, but then the A/C disengages and the RPM rises back to normal without any driver input. The cycle repeats every 15 seconds or so. There's good connectivity. When powered up, it's getting 12V, and when the A/C auto-diengages, 0V. Could it be as simple as a bad ground somewhere? Something else entirely?

Link to a video of the issue here:

Car is a 1972 454 4-speed with air conditioning. The A/C was overhauled two years ago to use R-134a, but I haven't noticed the issue until last week (of course, I haven't used the A/C in a while, either).

Any help is much appreciated!

Greg

That is your comperssor clutch cycling. It is the way it's supposed to work. If it's cycling too often you may be a little low on charge. The compressor does not stay engaged for the entire time you have the A/C turned on.

cfahey

Thanks for the response. When it cycles off, it does indeed stop blowing for that short period of time, so maybe related to a low charge. I'll take a look at that.

MBrianB

You can check the sight glass on the A/C dryer in front of the radiator on the passenger side. If air bubbles or foaming in the glass then you're low on charge.

2mnyvets

I am not sure the compressor on this vintage AC system cycles on and off. I would suspect the thermal switch on the AC box in the engine compartment. Look between the box and the right side fender wall. You should see a two pronged sensor about 2/3 the way down the box. Pull the plug and jumper those two wires. The compressor should stay on. That switch is supposed to open if the box temp gets below freezing. One of a few things could be happening. Either the switch is bad, your system is low on Freon and the temps are below freezing. or you have no air movement over the coil causing the temp to drop below freezing.

REELAV8R

2mnyvets

I didn't think my fist post showed up. So I rewrote it. Below has slightly more information.

I am not sure that the compressor cycles on-off on this system. I suspect the problem is the thermal switch. The two pronged switch (sensor) is located on the AC box in the engine compartment between the right inner fender wall and the AC box. It is located about 2/3s the way down the box. Unplug the sensor and jumper the wires as a test. The compressor should stay on. If it does stay on, your problem is either the switch or the box getting too cold. If the sensor is working properly, the sensor shuts off the compressor when the temp in the box is below freezing You will have to determine if the box is getting that cold.

F4Gary

So your blower fan stops blowing too? That's not right. It should keep running whether the compressor is on or not. Maybe it is your hvac panel.