AC Recharge DIY - what are the correct pressure and refrigerant capacity?

[German Engineer]

Hello everyone,
I have a 1999 Explorer Sport with the 4.0L OHV engine (Vin X).2WD.

I'm just in the process of recharging my AC system with one of these AC Pro kits that has a cheap gauge on a can and a little thermometer for the vents.

The three main questions I have at the moment are basically these:
1) what is the correct pressure on the low side that I need to charge the AC up to at around 75F ambient temperature?
Should it be at 35 PSI or 40 PSI or something else?

2) What is the correct refrigerant capacity of my system?
Is it really 30 Oz of R134a plus 9 Oz oil (39 Oz combined)?

3) Should I really go ahead and start adding more r134a from another can of or not?
- I'll get to this and the other question in detail below:


Here's the full story:
I got my Explorer 2.5 years ago used and in the past month the AC just wasn't as cold as it used to be.
Previously I only owned older German and French cars without AC so this is my first AC recharge attempt ever. So I went and got me this Ac Pro recharge Kit with the gauge and a 14 Oz can.

My compressor clutch was clicking on and off quick so I'm pretty sure my system was really low on refrigerant.
So I emptied the whole 14 Oz can, but never even got the pressure up to 30PSI. The compressor clutch stopped engaging and disengaging and started running continuously. So I went ahead bought another can and emptied that into the system 2 days later and the pressure on the low side when running on AC Max full cold full ventilation is still below 30PSI.

I must say that I don't trust the cheap pressure gauge on the kit much. It just seems to operate kind of awkward. But I don't have anything better to check the pressure And it does seem to give more or less reasonable pressure reading for static pressure when the car and AC are off, showing something between 60 and 150PSI. It is really hard to interpret any reading that high, because of the gage not really having any numbered in that range. But my best guess would be that it's probably somewhere around 100PSI, maybe even 130PSI.
Anyways, what I believe this static reading tells me, is that the gauge probably does work more or less correctly, even though it seems to operate a bit weird.

The car also does get much colder than before, now that the compressor runs permanently and doesn't cycle on and off anymore. On AC/MAX full power and windows shut I even managed to get as cold a vent temperature of almost freezing 35 deg. F.

But the issue is, that the pressure on the gauge is still just too low!
And I added two full small cans, one 14Oz and one 12 Oz making 26 Oz (22 Oz of R134a and 4 Oz of "additives" - which I guess are probably mostly oil) all together.

A Ford/Motorcraft chart which I found somewhere online says that any Explorer built in 1999 (no matter what engine) should be filled to a capacity of 30 Oz of r134 and 9 Oz of Oil.
But sadly, as so often there is no 1999 Ford Explorer Sport listed specifically. The Explorer Sports in the list only start after 2001. The list also has Explorers w/AUX (which I guess is rear AC?) listed after 2001 with 50 Oz capacity. I also read a comment somewhere online from someone that mentioned the Explorer Sport with AC for the rear seats takes more r134a than ones without. - But I must also add that I really don't know if there are any 1999 Explorer Sport without rear AC either.

So since I already added 26 Oz to the system and from all I could find the AC system officially is only supposed to be filled with 39 Oz (of r134a and oil) I'm now seriously wondering:

- Should I trust the cheap pressure gauge and really just go ahead and add more refrigerant?
Is it common for the Explorers AC system to take more than 26 Oz. if it was really low on refrigerant, but still running? If yes what pressure should I Ideally try to reach on the low side (at around 75F ambient temp)? 35 PSI or 40PSI?

- Or should I assume the gauge must be total crap and the readings of under 30 PSI can only be off? Should I better leave it as it is now, since the air inside the car does get much colder than before and I might end up seriously overcharging the system???
(I already got another 12 Oz can for 10 bucks, so it's not a matter of saving money either way.)

- Any other advice or tricks or ideas on what I could try or do to make sure I really get the system charged right?

Thanks in advance!

 

[ranger7ltr]

Folks in the A/C biz used to call those quick recharge kits "death kits in a can"...That being said the low pressure side of the system doesn't give you a good idea of what's going on...

Proper gauges should be used to measure the system and/or charge a system...And the capacity seems pretty close to what my 99Sport is running...The high side pressure should read 2.3-2.7 times the ambient temp at the condenser...With those pressures the low side will run at close to what the temp at the evaporator will be transferring to the warm air flowing across it...Now this is null and void if the system is not completely free of moisture and air which means using a great running vacuum pump with fresh oil in it and running it until the system is good and dry and holds vacuum for at least an hour...

My first question is why did the system leak down? Seals get old, hoses get crushed and moved, schrader valves leak, evaporators and accumulators leak etc Just adding to the refrigerant in a system and not fixing the leak you will get air/moisture in the system which will contaminate the oil and make the system run a lot harder and hotter than it should...Do not be fooled; the Ford system should cycle the a/c compressor clutch...If your compressor is constantly running it is beating the brakes off of itself and will begin the dreaded Ford "Black Death"...

If at all possible find someone with gauges...Good gauges that will give you proper readings...Then find where the leak is and fix them before doing anything else...Add your oil into the system and close it for the last time...Then when the system is sealed and empty run a long deep vacuum on it and verify it will hold that vacuum for an hour before doing anything else...If it holds for an hour you can ensure any moisture in the oil and the system boiled off and it is as dry as it can be...THEN add the proper amount of refrigerant by weight and enjoy being too cold air in your Sport...

To give you an idea of what to expect my Sport last ran last weekend with the air temp in the upper 90's here in Texas and the center vent sat at 35 degrees F in the middle of the afternoon...And the system has not been opened or serviced in the previous 5 years...Nor had I run the trucks' a/c since 2012...I had to get it inspected to get it registered and had to drive it but I was very cool and comfortable inside...

I wish you were in my part of Texas as these systems are bulletproof when they are serviced the right way...

 

[ranger7ltr]

What is with the line through the last half of the message??? I have never sent that before... Here is the last part of the above without the line...

If at all possible find someone with gauges...Good gauges that will give you proper readings...Then find where the leak is and fix them before doing anything else...Add your oil into the system and close it for the last time...Then when the system is sealed and empty run a long deep vacuum on it and verify it will hold that vacuum for an hour before doing anything else...If it holds for an hour you can ensure any moisture in the oil and the system boiled off and it is as dry as it can be...THEN add the proper amount of refrigerant by weight and enjoy being too cold air in your Sport...And the static pressure just tells you the system is equalized between the low and high side when the compressor is not running...There is no good meaning of the levels shown while in static mode except the system is holding refrigerant while the compressor is not running...

To give you an idea of what to expect my Sport last ran last weekend with the air temp in the upper 90's here in Texas and the center vent sat at 35 degrees F in the middle of the afternoon...And the system has not been opened or serviced in the previous 5 years...Nor had I run the trucks' a/c since 2012...I had to get it inspected to get it registered and had to drive it but I was very cool and comfortable inside...

I wish you were in my part of Texas as these systems are bulletproof when they are serviced the right way...

 

[German Engineer]

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Thank you very much ranger7ltr, one of the cans I put in says it has some dye added in it, so I will definitely get a UV lamp and check for leaks.

You say the compressor clutch should cycle on and off and the compressor shouldn't be running permanently the way it does now.
Before I added refrigerant it would cycle on and off all rapidly within just a few seconds, maybe 5 or so.
Only now after I added refrigerant does the compressor run continuously.
Does that "symptom" of the compressor staying on permanently along with the low pressure readings on the cheap pressure gauge indicate that I still need to add more refrigerant, because the system doesn't ever reach the upper pressure when it shuts the compressor off?
I found an old thread in this forum where shamaal mentions that on the Ac of a 92 Explorer the pressure switch should open below 24.5 PSI and close above 43.5 PSI ( A/C Compressor Doesn't Cycle Just stays On)

Right now, my AC system obviously doesn't seem to ever reach that high a pressure on the low side.
Could that be the reason why the compressor it doesn't cycle on and off now?
Should adding more refrigerant fix this symptom?

Or does this not really make any sense considering I already added 26 Oz of refrigerant and there should there likely be something else badly wrong?

I'll also go ask my local autozone store to try and see if I they have a set of manifold gauges I could rent or borrow from them to get readings on the high and low pressure side.

 

[ranger7ltr]

The biggest issue I would wonder about is how much moisture is in the system...And what your high side pressures really are...

Your a/c system is working to remove latent heat from the air that is blown across the evaporator...This happens by the compressor working the refrigerant into a low pressure liquid then pumping that through the evaporator and absorbing heat from the cabin air... That changes the low pressure liquid to a high pressure liquid that goes into the condenser...That liquid expands into a high pressure gas inside the condenser and then releases that heat and changes to a low pressure liquid in the low pressure or suction side of the compressor...And any air in the system is being compressed and not helping the system work...In fact it is working against what it is trying to do...

The low pressure switch cuts off[opens] the compressor when the low side [suction] pressure drops below 28-35 psi...If the pressure were to stay that low very long the condensation would freeze the evaporator coils and block airflow...But it cycling allows the condensation to stay liquid and flow out the bottom of the evaporator case and to the ground...It also keeps the airflow channels as clear as possible and lets the airflow get as cold as it can...The high pressure [discharge] side of the system opens somewhere above 300 or so psi to stop any damage to the system since pressures that high would mean ambient temperatures in the 115-135 F range, the radiator and fan clutch combo is not cooling properly, the refrigerant system has moisture and /or air in it, or the refrigerant amount is way too high and cannot change states as needed...Any of the circumstances will cause the high side pressures to balloon and the high pressure switch to open and protect the a/c system... There is also a pressure relief valve on the back of the compressor that will open when the pressure gets even higher if the high pressure switch cutout doesn't open and lets the compressor continue to run...

The quick cycling of the compressor is indication that the a/c system is dropping to the cutoff point too fast and not running long enough to absorb any heat from the circulated air...As the refrigerant level is increased, the system will run longer thus removing more heat from the air and cooling off the interior... You can tell when the system is getting "right" when the bigger line to the accumulator get cold and starts to sweat...Conversely the smaller line to the condenser will get hotter than hell to show the amount of heat being pulled from the air inside...

Unfortunately the only way to remove air/moisture from the refrigerant is to evacuate the system and pull a long hard vacuum on it...This will pull any moisture out of the oil in the system which if you open the system I would drain the oil and replace it anyway...Hopefully the leak, if any, are at the connections of the accumulator and maybe the front or rear seals on the compressor...Wherever they are if you fix them pull a vacuum and then recharge the system...I believe the amount of refrigerant for the Sport is 30 oz. of refrigerant and 9 oz. of oil...

 

[Terkins]

Hello, ranger7ltr. This is the first summer I'm approaching with my 2000 XLS 4WD. I use the A/C regularly due to allergies (vs. windows open.) I just passed 140K and only acquired the vehicle 09/17. The A/C "works" "OK" (it's Spring and temps aren't very hot yet in Central VA.)

I'm temped to get the A/C "charged" at a local shop but wonder "if it isn't broke: Don't fix it!" may be a better path? I can't afford major repairs and the vehicle doesn't have any known problems. Should I just "use it" and forget about trying to have it "charged"? ($30.00 "special" at a local shop)

What would be the best course of service to order to help "maintain" whatever A/C function I currently have...maybe improve-upon it? I'm simply trying to do preventive maintenance on the A/C, if there is such a "thing"?

 

[ranger7ltr]

What is your definition of "OK"? What vent temps are you seeing? If your shop is reputable they would outline how they would do what they do BEFORE you take it in and have them run up a huge repair bill...

Talk to them; ask them what issues they see with the system...Have them come up with a plan of attack IF they find anything wrong...They should come up with high/low pressures and ambient temps at a minimum...Most shops to do a recharge would remove the existing refrigerant and reinstall by weight especially on a system using R-134a or newer fluids...Anything else is a guestimate of charge level...And I would imagine they would be more costly than a $30 special...

 

[German Engineer]

On the progress of my current AC project:
I found out I can rent manifold gauges from my local Autozone. But due to lack of time, I haven't done that yet.

But I did also find a UV flashlight for $10 (from Rayovac) in the camping section at Walmart to check for leaks. some of the cans I filled into my AC have dye added.

Well, I couldn't find any leaks on the AC of my car yet. But I did find a MAJOR leak on the valve and gauge of the AC/Pro kit.
Turns out I basically just evaporated around 30 Oz of R134a straight into the air for $50 bucks.
I'll return the kit and try and see if and how much of the cans I can get refunded.

And now I'm also a little worried, I might have gotten a bunch of air into my AC because of the flawed AC/Pro Kit.

Well, at least the mystery why my AC "needed" so much R134a out of the cans is now solved.

 

[Dono]

Thank you ranger7ltr. This is great information.
I've had my motor out so many times, I have been recharging with red-tek.
The only really safe way to not twist a hard AC line removing the motor is to disconnect one large AC line that goes across the motor.

You taught me many things in this thread, including "Its time to change the pag oil so I know how much is in there and there is no moisture in it". My compressor is out, so its easy for me to drain and re-fill at this point.
I have a new accumulator and a variable orifice tube for when the motor goes back in again. I did notice the air wasn't all that cold the last time I recharged with red-tek. I do have the dual gauges and a vac pump to pull vacuum when recharging.

How do you feel about the red-tek, or any other propane based refrigerant? I'm a fan of it since I don't have to get the system evacuated when the motor gets pulled (I know I still should, but its not nearly as environmentally damaging).

Sorry about the hijack, but this seems like an appropriate question.

 

[eric mentzer]

my 1996 4.0 ohv ac system is giving me issues also, system held a 200 psi nitrogen pressure test no problem, sprayed all exposed fittings with soap, however when i pulled a vacuum it lost the vacuum in about 30 seconds. maybe compressor shaft seal. factory charge on hood sticker says 30 ounces 134A. if the leak is on the liquid side you will lose alot of oil and only way to tell is to remove compressor. my schraeder was leaking badly however i put adapter on with flare cap and still blew the charge somewhere. mine is cycling on low pressure switch as well rapidly. i wouldnt use any flammable refrigerant, but if no torch is being used on components i guess the risk of fire would be low. thought was illegal anyhow unless system held a pound of less or something ( alot of mini fridges use butane). next step if you dont see dye is gas it up and get a refrigerant sniffer to locate.

 

[ranger7ltr]

I have seen others use alternative refrigerant and have good if not great success...I believe the primary issue is the heat exchangers don't have the ability to perform the same change of state with propane and other fluids since the molecule size is different and the heat saturation is lower than standard refrigerants...I have seen ammonia used as refrigerant but the process is by far different than a standard automotive as these systems were used to cool whole buildings...Unfortunately I cannot add to the propane refrigerant use although others have made it work but did modify their systems to optimize their process...

On the system sealing there are lots of areas to check for a leak...My typical areas are the schrader valves sticking open, the seals on the hose manifold on the rear of the compressor, the compressor shaft seal, and the accumulator...If you don't find a leak then look at the condenser or the evaporator...Especially losing a vacuum in 30 seconds but holding pressure I would suspect a seal and in a system with age on it I would just change all the seals between hoses and fittings then try to pull a deep vacuum again...Also the vast majority of oil is in the accumulator and the condenser...The compressor holds very little oil...So if you lose a hose, high or low side, oil will fly out of the system big time and compressed air to the condenser and fixing the leak and adding oil back to the system before charge and vacuum will give you a good system lubrication...I also use Nylog on my seals and o-rings and a synthetic oil that is more heat resistance