Unusual A/C Compressor Issue

[tony1679]

I'm stumped. Vehicle is a 2003 Dodge Dakota 4.7L. I had a bad clutch on my OLD compressor. That was the only thing wrong, no internal compressor damage/debris. The insides were very clean. I had a trusted mechanic replace with a NEW (not reman) compressor, new accumulator/dryer, and new orifice tube. Vacuum pump for 1 hr, all was perfect. No leaks. Pag 100 oil and R-134a only (no stop leaks, dyes, added junk). System capacity is 30 oz. He added 36, and was monitoring gauges appropriately.

My a/c blows cold. But the compressor has been short cycling excessively. I took it back and asked if it was overfilled. He hooked everything up and said yes, but not by much (temp did go up about 8° from initial service). He let out about 3 oz. It still short cycled. So I let out about another 2 ounces on my own. Still no change. I only have a low pressure gauge, so I am half blind. But what I can see is when the compressor engages, it starts around 29 psi and drops quickly to about 24, where it stays for about 30 seconds before stopping. When stopped, it gradually rises to about 48-50 psi over about 10 seconds, then re-engages and repeats.

What could this be? I know this is a classic under-filled symptom, but if anything this is a little over. Bad compressor? Sensor? Still overfilled? I'm tired of not running a/c in 95°/90% humidity because I don't want to damage my new system. Thanks in advance!

 

[Lubener]

You may still have moisture in the system. I would have run the vacuum pump longer. I still cannot figure out why on a 30 ounce system the tech put in 36, too much and effiency goes down.

 

[WobblyElvis]

Without the proper tools it's going to be hard to diagnose. You paid for a major AC repair and it's not working right. I have to ask, why not take it back?

 

[Chris142]

If he does not have a ac machine take it somewhere that does.

 

[Chris142]

Why would he add 6 more ounces than it calls for? It's probly making too much pressure and triping that switch

 

[440Magnum]

Well, I agree that its probably still over-charged. Its almost impossible to correctly gauge how much you have released when you're trying to lower the charge, that's why its so important to charge with the correct amount in the first place.

Once you've got the charge spot on, then wen you are testing it, do you have the controls set for NORMAL A/C (not recirc) and the blower on maximum? those are normal test conditions. If it still short-cycles under those conditions, I'd suspect that perhaps its over-filled with compressor oil which is slugging the orifice tube, or it has the wrong orifice tube (or it clogged), or else a pressure sensor is kicking it off too soon.

 

[punisher]

If it was mine, and I just wanted a quickie diagnosis- Short/hotwire you low side pressure/cycle switch and see if anything behaves differently. If the compressor continues to short cycle with the switch shorted, look at either excessive high side pressures (excessive refrigerant charge/clogged orifice or condenser, insufficient condenser airflow) or a faulty high side cutout. Likewise if he compressor runs without incident, and you vent temps are in spec, you have a low side switch fault.

 

[MolaKule]

Interesting.

I just had this problem on my 1999 S-10.

It was the low side switch.

Clutch was cycling excessively even with 20 oz of added refrigerant.

 

[tony1679]

Originally Posted By: WobblyElvis
Without the proper tools it's going to be hard to diagnose. You paid for a major AC repair and it's not working right. I have to ask, why not take it back?
I have. He is trying to help me, and I'm trying to help him (and my compressor).
Originally Posted By: 440Magnum
Once you've got the charge spot on, then wen you are testing it, do you have the controls set for NORMAL A/C (not recirc) and the blower on maximum? those are normal test conditions. If it still short-cycles under those conditions, I'd suspect that perhaps its over-filled with compressor oil which is slugging the orifice tube, or it has the wrong orifice tube (or it clogged), or else a pressure sensor is kicking it off too soon.
The a/c was indeed on recirc. I will see if that changes anything. As far as oil goes, the compressor came pre-filled with oil, and he used approximately 6 ounces of PAG100 (8oz bottle, 1/4 left in it). I'm not sure what it is supposed to take, but I wouldn't think it is over

. The orifice tube was the correct one, and no debris was in the system. I agree, either still over-filled with R-134a, or pressure sensor. But I have absolutely no idea where the sensor is on my truck. Apparently my era of Dakota was a mixed bag of a/c setups. All I can find is the "A/C Pressure Transducer" on the high side line. Is this what would cause it? Also, something else I thought of, is there any way a relay could cause this? I don't think so, especially since it kicks on and off now, but I'm no a/c expert.
Originally Posted By: punisher
If it was mine, and I just wanted a quickie diagnosis- Short/hotwire you low side pressure/cycle switch and see if anything behaves differently. If the compressor continues to short cycle with the switch shorted, look at either excessive high side pressures (excessive refrigerant charge/clogged orifice or condenser, insufficient condenser airflow) or a faulty high side cutout. Likewise if he compressor runs without incident, and you vent temps are in spec, you have a low side switch fault.
Interesting, I will have him try this.
Originally Posted By: MolaKule
Interesting.
I just had this problem on my 1999 S-10.
It was the low side switch.
Clutch was cycling excessively even with 20 oz of added refrigerant.
Like I responded to 440Magnum, I wish I could figure out what/where these sensors are. I have heard one of them is on the accumulator/dryer, but nothing is there.

 

[tony1679]

I took it to another shop today. I feel I got fed b s but they said "the R-134a cans are useless. They are mostly air, with some freon inside, it sounds like there is now air in the system because of this. You should only add freon from a 30lb tank. Period. You need to do another evac and recharge, the PROPER way." And they wanted ~$200 to do it. I'm not a moron, I know that is way too much for that service. Thoughts?

 

[Brad_C]

You got fed [censored]. There is no air in those cans, and provided you purge the lines properly when you hook it all up there should be no air entering the system.

No substitute for a proper evac though, and that means using an actual electronic vacuum gauge and doing it properly. None of your venturi vacuum pumps or "just vacuum it for half an hour", but actual measurement (ie it got down to 500 Microns and held under 1000 for more than x minutes). No, those units *can't* be measured on the bourdon gauge built into your harbour freight manifold.

 

[spasm3]

No air in the cans. Now you can get air introduced if you don't purge the line once you connect the can, there is air in the line unless you depress the center button with something. ( nothing in your hand.) I use a phillips screwdriver held in a vice and depress the button a couple of short times before attaching to the low side port.

 

[Chris142]

I get $65 to suck it out and recharge correctly.

 

[WobblyElvis]

I have a manual that says the pressure sensor/switch is screwed into a fitting on the liquid line between the condenser and the high pressure service port.

 

[tony1679]

Well, time for an update. My mechanic wanted me to change the pressure switch. On my truck, it is in fact the transducer I mentioned above. It controls high and low. So I changed it. It brought a major change. No more cycling. BUT, although it was constantly on, it was only running at 15psi. I called him to inform him of the changes. He said now it needed more freon. I said wait, you want me to add it? I don't have gauges. He knew I only had a low side gauge. He said just add 1 can, at 15psi it is at least 1 can low (I did bleed pressure to try to eliminate the variable of being over-pressurized). After the can is added, it should be real close, and he would perfect the pressure if that was the case. In his defense, he is the type of person that tries to save someone as much money as possible, therefore he tries to get me to do the easy stuff, that way he doesn't charge labor. Like I said, although he may not be perfect, he is honest. So I add 1 can. Of course, I added it extremely slowly. It gradually raised the pressure, and near the end of the can, it got close to 40psi, but never exceeded. Keep in mind, I added this can when it was 94-97° outside and extra humid. Done. No cycling. Pressure was about 38-40. But I said yeah, I've been down this road before. I don't buy it yet. Let's drive it. Sure enough, I drive less than half a mile, and it short cycles again. Constantly. Now it won't stop short cycling under any circumstance. I called him back to explain, and told him I am done trying to guess. It needs fixed. Period. I feel I have gone above and beyond as a paying customer to help...

It may just be the pressure being out of whack at this point (because I am half blind using nothing but a low side gauge). But if he checks the pressure and says it is ok, what should my next step be (regarding both problems, what to do about my mechanic, and what part could be my problem)?

 

[Jetronic]

is your evaporator sensor reading low temps, causing the cycling?

 

[tony1679]

Originally Posted By: Jetronic
is your evaporator sensor reading low temps, causing the cycling?
...I have no idea. This is something I would have never thought of (limited knowledge of a/c systems). I will definitely look into this. Thanks!

Edit: what would cause that? Just a bad sensor?

 

[Jetronic]

bad sensor or bad evaporator valve

 

[tony1679]

Well yet another update, he hooked up his gauges to my truck yesterday. It was a freak 71° outside, high humidity. The low side pressure was at 24, the high side pressure was 140-150. He said it was in fact still low. So in goes another 2/3 of a can. This brought the pressure to 30 on the low, 170 on the high (I think, not positive). Whatever it actually was, he said it was perfect for the conditions. I told him I would drive 2-3 miles and return to see if it would cycle again (I knew it would). Sure enough, I was right. He finally realized I'm not crazy. So he re-attaches his gauges, and the pressure was lower (slightly) than before. Again, we are 110% positive there is no leak, and no restriction (that would cause the pressure to rise, not fall). So he added the extra 1/3 can. He said there was no possible way it could be undercharged. It was blowing ice cold, and the accumulator and lines were sweating profusely. He then started looking elsewhere. He noticed the A/C relay was VERY hot. So he switched 3 relays, example: A-B, B-C, and C-A. All 3 relays still worked. But once again, the A/C relay was VERY hot after the switch.

He is seeking a buddy's help, who is a Chrysler tech at a dealer. This guy really is going above and beyond trying to help me. We are both thinking either something is screwing with a relay, or the clutch is bad on the new compressor. But neither of us are sure.

What could possibly cause a relay to get HOT? Neither of us have had an A/C job become this difficult.

The only other thing I can add (which I think is totally irrelevant, but who knows) is that I know for a fact I have an interior issue. I think it is a blend door or the actuator that operates it. It blows cold when it should, and it blows hot when it should. The fan speed is also correct. 1-2-3-4-3-2-1, all is good. But the A/C when on the "head" setting blows from both the head and defrost. When the heat is on, when I want it on defrost, it blows from both the defrost and the feet.

Am I correct in saying that while this is an issue (that I do plan on correcting), it has no effect on the compressor malfunction, and is only an annoyance to me?

Thanks to those who are following this and thanks for the help!

 

[punisher]

Originally Posted By: tony1679
What could possibly cause a relay to get HOT? Neither of us have had an A/C job become this difficult.

But the A/C when on the "head" setting blows from both the head and defrost. When the heat is on, when I want it on defrost, it blows from both the defrost and the feet.

Am I correct in saying that while this is an issue (that I do plan on correcting), it has no effect on the compressor malfunction, and is only an annoyance to me?


Relays get hot, electricity will do that. Put a DC clamp ammeter on the relay pwr out to the clutch and see what it is pulling, or OHM the PWR out from the relay connector to ground and see if there is too low a resistance. Could be something weird like the clamp diode in the clutch circuit leaking, but that is strictly out of left field (and that diode would likely burn up).

Check your vac connections under the dash, as well as the main vac line to your AC control head for your air direction problem. If by chance you have an all electric blend door/air handler, then diag gets tricky. At this point it is just an annoyance.