The A/C in my 2003 still works, somewhat. Not as good as it used to. I've noticed that even on max, the clutch cuts in and out, roughly 5 seconds in, 10 seconds out. My research indicates this is a typical symptom of being low on freon. (Correct?) I used a blacklight to check for leaks (dye) and did not see any. I've had the truck for 9 years and have never serviced the A/C. It has 190K miles. I am guessing and hoping that there is just a very slow leak and it has just gotten low over the last 10+ years. And so I was hoping I could just add a can or two of R134a myself. My mechanical skills are medium and I'm sure I can handle adding freon, but will not attempt any sort of major repair or overhaul, and really really don't wanna take it to a pro ($$$) if I don't have to.

Thoughts? Comments? Suggestions?

 

Yes, sure give it a try, there are R134a cans that have a 'no leak' additive that swells o-rings to stop slow leaks, wouldn't hurt anything to use a can of that, only costs $1 more usually

 

In my limited experience compressor kicking on and off "cycling " is more likely too much freon, not too little.
high and low pressure switches. If your pressure is below 25lbs the compressor just wont kick on at all. But if the pressure is too high it will kick on. But when it kicks on it increases the pressure that triggers the high pressure switch so it kicks off. Pressure drops opening switch so compressor kicks on again, etc...

 

Well, from what I've been reading--- pressure too low or too little freon causes the same problem, for pretty much the same reason. The ECU turns on the compressor (clutch), doesn't sense as much pressure as it expects, and so turns it back off. Then after a bit, tries again. Can't see how the pressure would be too high though or how it would have too much freon since nothing has been done to it for at least 9 years.

But thanks for your input though!

 

The AC I rebuilt was in a 1994. Maybe things got more complex since then? In mine the ECM only monitors wide open throttle. It kicks the compressor off in that state based on input from the TPS. The other two inputs are a low pressure switch on the low pressure line side. And a high pressure switch on the high pressure line side. Both switches are there to protect your compressor. Either from too much pressure blowing it up or it running dry from a leak. Both switches are normally closed (completing the circuit) until they sense pressure too low on the low side or too high on the high side. Then switch opens and breaks the chain. Problem with pressure too low isn't the lack of freon but oil. If freon leaks out it takes the PAG oil out with it.
maybe Ron or someone can weigh in? If systems got more advanced in a decade? low pressure means a leak. High pressure is usually from adding too much. Maybe a clogged orifice? Thatd be my only other guess for pressure too high if you've never added freon. If that's the case it's a cheap easy fix. Orifice tube is maybe $10. Only problem is you need to evacuate and recharge the system to replace it. Its inside the AC line. Also I have heard some compressors have a temperature sensor for overheating.

 

As far as diagnostics, I'd start by checking the pressure. If you have access to a manifold guage that's great or some freon cans from auto parts stores have a low side guage. That is enough to get some basic idea. Check low side pressure with engine off. Then check with engine and AC running. See how high or low it's going as it cycles.

 

If pressure seems in normal range of check the relay. Try plugging in another one. Not likely because with bad relay it usually just stays off. But it is an easy enough check so why not? Then I'd check the low and high pressure switches themselves. Could be a faulty pressure switch. And those are easy to change. Just screws onto a Schrader valve so no need to evacuate the system. Pull electric plug off and paper clip the wire start car and AC see if cycling stops. Careful paper clip doesn't touch body or fuse will pop. That test will let you know what sensor is triggering it. You can test the switch if you know the pressure is right you can test for continuity across the terminals. At least on my old 94 system there are only 2 terminals. If there are more than that find out what they are before doing paperclip test.

 

Also another problem I believe if the pressure is significantly low. Those freon refill cans dont have oil in them. And that's what kills compressors. You can get it working by topping the freon off but it will still be short on pag oil. Only way to refill that is to evacuate and start over from scratch like they do at AC shops. Pump it all out then pour in the prescribed weight of oil. Then the prescribed weight of freon.if you lost your freon from a leak and sealed leak with a freon stop leak product. Your compressor will be on borrowed time. If its completely empty you can pour the pag oil into the top of the accumulator where the top AC line connects with a funnel.

 

I bought a can of "freon" refrigerant R134a which includes a low-side pressure gauge, but I haven't hooked it up yet. The can also supposedly contains some oil, dye, and leak sealant*. Good idea to test the 2 pressure sensors, I will do that as well as checking the low side pressure. I also considered the possibility of a clogged orifice tube. Evacuating and recharging the system is out of my comfort zone but turns out I have a friend who has a full manifold, vacuum pump, and other necessary equipment and experience to do it. (Retired appliance repairman, including fridges and window A/Cs) Unfortunately he lives out of town, but fortunately he is coming to visit in a couple weeks. He also gave some good advice such as when the tube leading into the condenser gets condensation on it, the pressure / refrigerant level is reasonably close, but if it gets frost, there is too much.

* a little skeptical about that since the refrigerant is a gas and the oil is heavy dense liquid. Seems like it would be difficult to inject both at the same time (?)

 

I'd be careful with what you're doing. I work residential heating and cooling and most people don't know what the **** they are doing when it comes to air conditioning. If you have a leak you need to fix it, there's no way around it. Also you were right, the compressor is cycling on the low pressure switch. It's possible it is cycling on a high pressure switch but less likely. You really need to find the leak and repair it, evacuate, and recharge to OEM specification for weight of refrigerant. That being said, this could be an entirely different problem and we have no way of knowing without a proper gauge manifold reading while its running. I need both the low and the high side pressures as well as the outdoor ambient temperature and the AC running full speed. Report back with these findings, I can interpret.

Just so we are clear i did just that with my own truck, and actually retrofitted a diffferent refrigerant altogether (I do NOT advise this unless you are a professional). R12 is expensive and harder to come by so I used R409a and calculated the new weight for the system. Air blows ice cold in the middle of summer.

Leak stop cans are a joke, don't bother with it.

Also, one easy way to find leaks is to look for oil residue around the refrigerant piping. Common places are where they join together, for example the flare nut fitting on the reciever. I had reside around that area and sure enough a refrigerant leak was right there.