• Welcome to The Truck Stop! We see you haven't REGISTERED yet.

    Your truck knowledge is missing!
    • Registration is FREE , all we need is your birthday and email. (We don't share ANY data with ANYONE)
    • We have tons of knowledge here for your diesel truck!
    • Post your own topics and reply to existing threads to help others out!
    • NO ADS! The site is fully functional and ad free!
    CLICK HERE TO REGISTER!

    Problems registering? Click here to contact us!

    Already registered, but need a PASSWORD RESET? CLICK HERE TO RESET YOUR PASSWORD!

A/C needs a charge

Burning oil

Burning oil

LeroyDiesel.com
Vendor
Messages
10,306
Reaction score
1,958
Location
Houston
Its getting hot again and the past couple days I have needed A/C.
I wanted to check with the experts to see how you do it and how do you know how much 134 to add and if I am doing it right.

I have allways hooked up the gauges with A/C on high, low side needs to be 30 psi and high side not over 150 psi. I add 134 until low side is 30 psi and call it done.
Am I close?
 
Burning oil said:
Its getting hot again and the past couple days I have needed A/C.
I wanted to check with the experts to see how you do it and how do you know how much 134 to add and if I am doing it right.

I have allways hooked up the gauges with A/C on high, low side needs to be 30 psi and high side not over 150 psi. I add 134 until low side is 30 psi and call it done.
Am I close?
Click to expand...

High side/low side pressures are strictly dependent on what the ambient temperature is. The higher the ambient temperature is, the higher the system pressures are going to be (both low and high sides), and the lower the ambient temp, the lower the pressures, -etc. There are cross-reference charts available online that show pressures versus ambient temperature for various refrigerants.

I know that my extended cab system holds 2-1/2 pounds. Quad cabs and/or burbs will likely have a higher capacity (for reference only).

For obvious reasons, if your system is stone dead, it really should be vacc'ed out. Additionally, there is a dessicant filter that can become skunked up if the system has "seen" atmospheric pressure and moisture in the air has been allowed into the system.

I'm not an expert, -in fact, I know just enough to be dangerous!

But, I did stay at a holiday-inn express last night. ):h
 
^Agreed. If you've got gauges, I'd get a vac pump. Now cheap from Harbor Freight. No guesswork there. I'm not as sharp as I maybe once was on the AC stuff, but IIRC, R134 is a little more finicky due to being a larger molecular size.
 
Mine is still holding a small charge. It blows cold, but the comp cycles alot. Usually that means low freon.
So, while adding r134 what do you guys watch for on the gauges?
 
pull your blower and check the evap fins too... mine runs worlds better after cleaning it. freezes me out. and smells better too!
 
If it's at least 70 out, look for the accumulator/drier to sweat with the fan on high. That should put you close.

Would be best to have what as said above and the leak fixed.:thumbsup:
 
Burning oil said:
Mine is still holding a small charge. It blows cold, but the comp cycles alot. Usually that means low freon.
So, while adding r134 what do you guys watch for on the gauges?
Click to expand...

Nothing. You cannot fill a system by the guages. As was mention ambient temps as well as the slightest rpm change will affect readings. There are no "set" readings to charge it. It's more about the differential between the nigh and low side as well as pressure being with in accptable range. As far as Optimum charge remember this:
NEVER OVERCHARGE a system It will not make it colder. it will make it warmer and work harder. That said the industry standard is to use a reclaimer and evac the system and then recharge with the appropraite measured charge as per mfg spec.
Of course since most of us back yard mechanics don't have access to a 5,000 Reclaiming /charging station the best thing for you to do given what you describe it to close all the windows, let the a/c run on max and with all ducts closed but the closest one to the evaporator. Stick a thermometer in that duct and very slowly, patiently add small amounts of freon untl the temp at the duct is somewhere between 54 to 39 degs. 39 is optimal but you'll probably not see it on a gm system, espcially r134a. Older systems with the giguno 10 cfm Harrison compressor that took like 30hp off your motor and r12 could get that cold. 55 is weak and means there is probably something wrong but it's passable. Ideally on a gm like you have somewhere mid to high 40's is what you should see. Remember you need to add small amounts and wait. it won;t just drop the needle in two seconds. I have done many many GM systems as well as others. If all of a sudden the temps actually go up, you have put too much in so don't get greedy. If you hit 46-48 degs I'd leave it. Remember, a little low on the charge won't hurt it but overcharged will.
 
As far as leaks go, if you have not used it all winter and it's a half a pound low it's probably leaked out the compressor seal from non use. If it has a more serious leak the fastest way is just like porkin a fatty, gotta look for the wet spot. Dust will usually cling to leaks. If not a sniffer is my next recommendation. I personally do NOT like tracer dye but sometime if a leak is stubborn it's the only way. Stuff has gotten better since the old days. Years ago if a car came into my Dad's shop and someone put tracer dye in, he'd turn them away.
 
Let guages equalize with engine off. With 134 the low and high pressure side should read roughly ambient temp plus or minus. This will get you close. That is if you don't have a thermometer that goes low enough. I would rather see a touch lower than ambient.
 
Thanks, with all this info I should be able to get it done. Thanks for the links, I will check them out next.
I have cleaned the evap coils on my 93 and it did make a difference. Need to clean this one also. I used a special cleaner made for evap coils.
 
I would take it to a shop to have the freon removed. All of it. Then you can add the proper 2.5 Lbs of freon. R134A may be different as the 2.5 LBS is on my R-12 sticker. They also have a bigger condenser so go by the sticker or the book for your year. Oh yeah stupid GM puts this sticker on a replaceable accumulator so you may not have a sticker.

There is no other way to properly charge a CCOT system than by weight. NONE! That is empty system at full vacuum and add 2.5 lbs +- .5 lbs. 3 12oz cans is 1/3 lb short. 16oz to a lb.

If you get really cold air the system is likely low on freon. This low charge does not bring enough oil out of the evaporator and the compressor burns up.

Adding a small oil charge does not hurt. 8 oz is system capacity.

Check that your cooling fan clutch is good. The AC can cycle on high side over-temp/pressure. Overheating the AC system due to bad fans or plugged airflow is often overlooked.

A extreme performance improvement is to get a variable orface tube. This will make idle A/C performance cold! They are not 99 cents but around $20.00 and worth every penny.
 
A little low will NOT damage the system as long as the sensors are in place. That is why his is cycling so much. Like I sad before Starting from scratch is the best way but it can be done without doing that. It takes time. I have never had one fail in more than 20 yrs of doiing it. Some guys used to claim using a ford orifice made it colder. Never tried it myself. It can't go below 39 or it will freeze and blow the compressor anyway.
 
Pillow said:
??? Please explain what this is. I am lost... But learning a lot :)
Click to expand...

This site will give you a migraine headache as to what it does and why:

http://www.imcool.com/articles/aircondition/VOV2.php

Short answer:

http://aapak.com/Qstore/p000047.htm

This VOV is designed for climates with ambient temp. 105*+


The Smart VOV (varible orifice valve): uses system pressure and refrigerant flow to move a metering piston relative to a fixed opening in the sleeve. The piston movement is resisted by an attached spring.

You can notice:
Improved performance when converting from R-12to R-134a
5*-12* colder air (at hot idle)
Reduced compressor load and extended compressor life
Improved city fuel economy and emissions
Improved performance in factory R-134a systems
 
WarWagon said:
This site will give you a migraine headache as to what it does and why:

http://www.imcool.com/articles/aircondition/VOV2.php

Short answer:

http://aapak.com/Qstore/p000047.htm

This VOV is designed for climates with ambient temp. 105*+


The Smart VOV (varible orifice valve): uses system pressure and refrigerant flow to move a metering piston relative to a fixed opening in the sleeve. The piston movement is resisted by an attached spring.

You can notice:
Improved performance when converting from R-12to R-134a
5*-12* colder air (at hot idle)
Reduced compressor load and extended compressor life
Improved city fuel economy and emissions
Improved performance in factory R-134a systems
Click to expand...

Thanks WW, for the VOV info. Im going to use that on my 94. I just came back to this thread because I thought it had info on what to use to flush the system. I seem to remember someone saying to use denatured alcohol? Is that correct? Remember also they said the A/C flush is a rip off.
Any info on that?
I am going to be r&ring this weekend, new Comp, Dryer, orfice tube VOV. The compressor is making noise. Do you think flushing the evap and condenser is do'able?
Any other suggestions.
 
I use flush. Don’t care if it is a ripoff or not, I don’t use it that often… Not seen an issue flushing our condensers vs. the black death Ford has. You may add a extra inline filter if your compressor put a lot of junk in the system. Never added a filter myself.

Noisy compressor that is ‘hammering’ needs to be replaced. Otherwise it will just keep putting junk into the system before it locks up. This noise you can hear in the cab when it is really bad.

Pour 8 oz of oil in the new accumulator before install. Ester ‘oil’ for R134a conversions works well.
 
Got the new oil allready, waiting on the Compressor to come in.
Any problem using something else to flush the system?
 
You must log in or register to reply here.
Back
Top