A/C Compressor Issues
 

I've got about 150k on the truck, and a stock alternator. Just recently it started kicking in every 10 seconds or so - but seems to only engage then disengage.... just enough time to bog the engine for a second.

Any thoughts on what could be causing this?

Are you sure it's not the A/C? A system with low ref. in it makes the clutch pop in and out just like you describe.

Rich

I only took a quick look last night - the truck is still new to me too.... but its the acc thats closest to the battery, I didnt see any a/c hoses coming out, but just a few wires. I didnt follow the wire, but it does look like other alternators that ive changed out.

But, I only checked for a second.

Also, havent used AC on this truck yet at all.... so the compressor shouldnt be engaging.

Yea, youre right. It's a '94, would I have to change the type or ref?

i belive so....i think they still used the old stuff in '94....

If you have the controls in a setting that calls for air conditioning and it is not really hot outside, the compressor turning on and off a lot is relatively normal. Once it gets hot outside and the thing actually has some work to do, the duty cycle will get longer.

Rapidly turning on and off and not making the air cold is a sign of low coolant and you'll need service for the leak and recharge.

I've tried for a while to get it to engage on command; you know, try to figure out why its engaging. From what I see, its happening at idle only, and about every 30 seconds or so, for about 1 second engaged at a time.

I haven't really tried running the AC to see how that works, it should have been one of my first steps.

ok, put the thing on an AC mode. If it turns on for a second and shuts off, you need to take it to a shop that will service your AC system. Your coolant is low or gone.

1994 Ranger 4.0 = R134A
 

My 1994 Ranger has R134A refrigerant. Put you slide control on defrost and see what the compressor does. Anytime you use defrost the compressor runs to remove moisture from inside the truck and off the windows. If the refrigerant level is correct/close the compressor will run continuously.

This will give you a ballpark idea if you have adequate refrigerant operating on a/c: The compressor may kick off and on at idle if you are not running the fan at high speed. Low rpm, low fan speed translates into low refrigerant pressure which will cycle the compressor on the low pressure switch causing the clutch to cycle. Put something on the accelerator to run the engine about 1500rpm and turn the fan to high and control to max a/c. If the refrigerant level is correct/or close the clutch will stay in operating the compressor. If you run it like this for a while and it is cool outside once the inside of the truck gets cold the compressor will start cycling on the low pressure switch again. Low temp=low pressure and cycling occurs. If ambient temperature is mildly warm to hot the compressor will/should run continuously. If you are not familiar with a/c operation do not attempt to charge additional refrigerant yourself unless you understand what you are doing. I know a guy who put the low side hose on the high side valve and the high pressure blew the bottom of the 14 oz. can off and broke his foot. He was lucky the rush of liquid refrigerant did not burn or blind him at the same time. I've serviced many vehicle a/c's in the past 38 years and I still do a checklist everytime I service one.

Warning: The high pressure side of the system will at times run extremely high pressure so if you are not familiar with operation and service take it to a pro.