I have a "pulsing" problem while idling in my truck. As someone suggested I checked the alternator by disconnecting the battery with the engine running and accelerating a bit (with the car stopped, in "park" and e-brake engaged). Anyway, the truck ran fine and the alt needle went to the "charge" side of the gauge and stayed there. It actually did much better than with the battery connected.
When I went to reconnect the battery, I noticed a strange clicking noise while the engine was running. I connected the battery and saw that the AC compressor was cycling off and on when the click sound happened. The AC was turned on in the cab. Also, the compressor makes some strange noise when engaged. I took a short video of it.

YouTube - f150_ac_comp1.MOV

I also took a video with the AC turned off. to show the difference. It runs much more smoothly of course. I'll take it out and see if the idling problems still occur. (please ignore the ice cream truck music)

YouTube - 101_6461.MOV

BTW, I've been having issues with the AC not working too well. Lately it's gotten much worse and it barely blows cooler than the ambient temp.

Any input from those who know?

Thanks

 

Your AC system has a refrigerant leak. Because there isn't enough
refrigerant to operate properly, it is causing the compressor to short cycle.

 

Thank you, I'll take to a shop tomorrow and have them look at it. Is it possible that the switch which controls the clutch might be bad?

 

If the low pressure/clutch cycling switch goes bad it usually prevents the compressor from ever turning on. There are exceptions, but for the most part the switch usually becomes an open circuit.

 

Thank you for the input. It's interesting that the compressor engages and then disengages for no apparent reason. I say this because I had the freon checked just a few weeks ago and the guy said that it seemed OK and there did not appear to be any leaks.. Of course, it could have leaked out since then and obviously the system has not been working very well for quite some time (that's why I took it to have the refrigerant checked). I hope I can get the AC working right and not have to spend a small fortune in it.

 

You didn't say what year your truck is.

Here's a picture of the Accumulator used on 87-91's that shows the location of the low
pressure cycling switch which controls how long the clutch compressor
stays engaged once you turn on the AC.

To eliminate that switch you unplug the two wire electrical connector at the
Low pressure cycling switch. The switch is screwed on to a schrader valve
which is circled in red in the picture.

With the electrical plug disconnected, use a piece of wire or paper clip and
jump the two wires at the connector together. This bypasses the cycling
switch. Start the engine and turn on the AC. The compressor clutch will
stay engaged. If the system doesn't cool, that would indicate you're low
on refrigerant and is why the low pressure cycling switch is cycling the
compressor.

 

It is designed to cycle off and on. When the temperature and humidity are high the compressor may stay on all the time. In somewhat cooler weather the compressor will cycle as it is designed to do.

 

OK, I took the truck this morning to the shop (BTW, it's a '94 F150 XLT, 5.0 A/T). They hooked it up to some device and after about 45 minutes they called me back to say that the compressor was leaking. They quoted me a price to replace the compressor, dryer and orifice. They are usually pretty high with their prices, specially the parts. I don't mind people making a living and a profit over their expenses. OTOH, I have to watch my pennies too since my income was severely reduced last year. Anyway, here is the estimate, what do you guys think?

 

I forgot to mention in the other post. They said that the reason that it was cycling like that was because it was building too much pressure. Of course, that's confusing to me because if it's leaking, it makes more sense that it wont build up enough pressure, but what do I know......

 

If the compressor is leaking at the connections, then I would not replace the compressor, just replace the o-rings on the connections. If it is leaking around the shaft, then replace it.

I just replaced my compressor, dryer, orifice tube, and all o-rings and spring clips on my 87 F-150. The only problem I had was finding a vacuum pump to vacuum the system out after I installed everything.

I spent less then $400 total on the whole install, which included $80 for someone to vacuum and charge the system.

You can save some $$$ if you buy the parts and install them yourself.

Hope this helps.

 

Go with carter's advice, replace the O-rings and try the system again. I replaced my own Evap and did some other work, including de-infectation to make my A/C operational again, the total spent didn't reach 150$.

 

Yes, I think I'll try to do it myself or get another estimate. They want almost $1K and that's way too much. I never will get that out of it, Of course, here in Atlanta going without AC is not a good option.

 

Ask them where the compressor is leaking. If its leaking around the hose connection then I would just replace the o-rings, vacuum, and recharge the system. If they say the compressor shaft seal is leaking then its time for a new one. In that case, I would replace the drier, orifice tube, and all the o-rings at all the hose connections.

I can not see replacing the compressor if it is not leaking around the shaft. I would still get a second estimate and see if they tell you its leaking at the same place.

 

I don't think they would tell me to change the compressor and all the other parts if it was not leaking from the shaft. They are high on their prices but I don't think they are unethical so I believe that the compressor is bad (unless they made a mistake in the diagnoses). I have another friend who owns a repair shop and he owes me some favors. I will ask him to price it and see what he says. At least he can get me the parts at his cost and that's great help