AC Low presure fill questions.

[Bizzy]

Ok so I have a kit that I picked up today from walmart. The gauge on the kit reads 45 when the car is off. Now with the car running and the AC compressor cycling, the gauge starts at 45 (helms says this should be 50) and drops to about 23-25 or so. Then the compressor shuts off.

From what the directions on the AC kit say, that the 45 (50) is where it should be all the time when the compressor is on. Correct? So then I'm thinking that the low pressure switch is triggering the compressor to cycle very often like that. Which means I want to add my can of stuff to bring it up so that it is in that 40-50 range when the compressor is running right?

rangerj where are you.....you seem to be have the answers to most of the A/C related questions out there.

<small>[ April 24, 2003, 07:27 PM: Message edited by: netviper ]</small>

 

[BlackOnBlackATX]

the low pressure side (which is where you will be filling it) is near the firewall. im sure youll find it when you poke around a little. i converted mine last summer. works great!

 

[rangerj]

Netviper,

I'm here buddy. You have a 94 with R-134a refrigerant right? Your compressor is being shut off by the low pressure switch. You can jumper wire the switch wires to be sure.

From the gauge reading you are getting it would seem that your low pressure switch is set at about 25psi.

Add a can of R-134a (one with some oil, but no more than one or two ounces). You are right, the low pressure side should be around 50psi.

Put an A/C thermometer in the center of the dash, in the vent, and shoot for a temperature of 40 degrees F or less (34 to 36 is ideal). The high pressure side should read about 250psi.

The temperature gauge is available at Auto Zone for a few denaro, and you can borrow a gauge manifold set from them for a deposit.

If your pressure is down you have a leak. Look for the wet spot of black oily dirt around all connections and on the condenser core. Eventually you will have to fix the leak, but if you can charge the system and get through the season, why not.

As stated above the low pressure side schrader valve for charging is back by the firewall. As a warning to ALL WHO READ THIS. DO NOT EVER ATTEMPT TO CHARGE AT THE HIGH PRESSURE SIDE.

A/C high pressure side pressures can get in the range of 400 psi to 600 psi. A pressure spike into a can that is already under a lot of pressure would turn the can into a deadly bomb!


One additional warning to ALL WHO READ THIS. A/C refrigerants boil at temperatures in the -200F range. If the liquid were to get on you it would mean instant frost bite. Think about your eyes, please. Work safely, and take working with these products seriously.

I understand you have a parts car. I'm looking for a Gen I (90) under hood (engine) wire harness (complete). Please e-mail me. rangerj

 

[sdpatt]

Your analysis is correct. The cycling switch disengages the A/C compressor clutch when the suction pressure drops below the cut-off. This is to protect the compressor. The system should be charged such the pressure maintains approximately the 45-50 psig during operation.

The target pressure is dependent upon the refrigerant and the ambient temperature. The pressure gauge should have a temperature scale on it also. The higher the ambient temperature, the higher the pressure. Just like tire pressures, it follows the gas expansion law.

Be careful not to overcharge the system. This reduces cooling performance because it increases the pressure downstream of the expansion orifice so much that the designed gas expansion and heat transfer is not achieved.

 

[BlackOnBlackATX]

if i recall, my autozone kit came with a nice guage to attach to the low pressure side to see how full it is. it also came with all the refridgerant, etc. i recommend the kit, only about 30 bucks if i recall.

 

[Bizzy]

well after reading these posts I went outside and took a stab at it.

I ended up adding 1 14oz can of Interdynamics R-134a Refill & Treatment w/**** cool - This can comprises of 11oz of r-134a and 2oz of Oil along with some cleaner & leak sealer.

After adding that 1 can my AC system would now be at 47psi while the compressor was off, and would drop to just under 25psi while running w/the AC on full blast. Outside temp is a nice 65F today. Now It would still cycle off down low there, and since it was running at the 25psi range I said to myself that it is still low. So I ran out and got some more R-134a.

I then added a can of straight R-134a with Leak Sealer from Interdynamics. After adding that can, the compressor still cycles on and off, but only when the AC is on a low fan speed in the cabin. On full blast it never cycles, and the PSI on the low side stays at just about 25-27psi.

So I'm thinking that I still need more refridgerant till I get it up into the 40+ PSI range while the compressor is operating. At this rate it would take about 3-5 13oz cans of stuff to get it to that point. I'm not adding anything else just yet to the system cause I want to watch it for a day or two to see if the pressure holds.

No I have a leak at the junction of the tube down by the acc/dryer thingy, but it appears to be an o-ring issue I think. Considering that I have only spent $13.00 on AC stuff so far I'm gonna wait and see if my AC goes south again before I thing about fixing the O-Rings. I know where it was leaking cause of the oil residue around that AC line fitting.

So Am I correct in thinking that my A/C compressor should not be cycling on and off becasue of the low pressure switch? Is it supposed to stay on all the time while driving when the A/C is on?

Also that I should prolly add a few more can's of straight R-134a till the operating pressure with the AC engaged is in the 40's, provided that the system don't leak all of what I just put in there out in the next few days?

 

[rangerj]

NETVIPER,

The system hold about 28 to 30 ounces of refrigerant. You added 11 ounces and another can of 8 ounces?

The compressor will cycle off and on as needed depending on the temperature. If will stay on in the defrost mode, and in higher ambient temperatures. The A/C is not needed much at 65 degrees!

What is the air temperature coming out of the center vent? rangerj

 

[Bizzy]

temp comming out of the vent is 38F to 45F with a 66F outside temp. I figure that when it gets hotter outside then the vent temp would go up a little while dealing with the hotter air.

I added the first can that had r-134a, oil, and some cleaners and sealers. THe can said that it had 11oz of refridgerant. The second can was a 12oz can of R134a w/Leak Sealer. So I figure that it was another 11oz of refridgerant and some more sealer stuff.

That would bring me to a total of 22-23 ounces of R-134a in there.

Previous to me adding the 2 cans of stuff, the pipes never got cold at all. Now then get pretty cold, but it's not unbearable to put my hand on. Now my 95 SE has always had a killer AC system, that thing builds up ICE on the pipes in this weather if the car is sitting still. Tested that one today and it was at ~45psi when the compressor was running, compared to my SHO at ~27psi now. I don't put much stock in the gauge that came with the interdynamics kit.

I believe that the system was completely empty due to the o-ring leak I have on the hose that leads away from the bottom of the Accumliator. I'm gonna see if that keeps leaking or if the sealers and o-ring conditioners help. Worst case I've wasted $13 bucks, but I think that even in it's state right now it would get me thru the summer and my trip to FL. If it all leaks out over the next few days I'm gonna be replacing those o-rings and charging it up again.

If the system holds it I think one more 12oz can of R-134a should be just about right. If the system was completely devoid of r-134a then is the air that was in there going to cause a problem over the long run? If I do have to replace th o-rings at the site of my leak, I might jsut pull the acc/dryer and heat it all up, then hook the system up to a vac pump and get any moisture out of the system. Any chance that I might have lost more than the 2oz of oil that I replaced? Or is there usually more than enough in the system to keep the compressor healthy?

I feel like I should write an article for shotimes from all this info, experience, and help from here

<small>[ April 25, 2003, 10:04 PM: Message edited by: netviper ]</small>

 

[rangerj]

Netviper,

Your system could not have been completely empty for the following reasons;
1. you had some pressure, but not enough to keep the A/C clutch engaged,

2. If the system was completely empty the low pressure switch would not have connected or turned on the A/C clutch, period.

If your leak was more severe you would see A/C refrigerant oil dripping, not necessarily a lot, but enough to drip. I do not think you lost any more than 2 ounces. This is a judgement call.

If the system was devoid of moisture at the time of its current charge, and it has not lost its complete charge (it has not)it should not have much (if any) moisture in it.

If you have to repair the leak, then the system should be vacuumed properly before putting in a fresh charge.

If you have any doubts about the amount of oil in the system you can do the following (recommended);

1 Remove the compressor and drain it into a container. Measure the amount of oil.

2. Look up, in the Helm shop manual or other resource, the amount of oil that is in the condenser, evaporator, and each line. Add the amounts and subtract the amount from 7.75 to 8 ounces.

The difference is what should be in the compressor. E.g. if 3.5 ounces are normally in the components, other than the compressor, then 4.25 to 4.5 ounces should be in the compressor.

Too much oil, as well as too much refrigerant, will reduce the efficiency of the system. If I remember right your system is set up for about 35 ounces of R-134a. Check a manual source for the exact recommended amount.

If you are going to go through the trouble to remove the accumulator/dryer, then do yourself a favor and replace it. If you have to open up the system consider replacing all of the "O" rings and garter springs. Just a thought! thumb
rangerj