Automotive Air Conditioning Information Forum (Archives)

BIG on Fri March 21, 2014 5:23 PM

Year: 97
Make: Ford
Model: F250
Engine Size: 7.3
Refrigerant Type: R134

My F250 A/C isn't cold after turning it on for the 1st time since winter. I'm in Texas and it's time to run the air again as it's already 77F today and humid. The compressor isn't cycling at all so the system appears to be low on refrigerant. I've owned the truck for 3 years and the A/C has been perfect but apparently has a very slow leak and is low enough the switch has the compressor cut out.

Given the system has always worked perfectly, I really suspect a very small leak. I have a good set of gauges with low & high side hookups. Is it not wise for me to just add a portion of a can of R134 until the system is cool again? I've posted on this site before with good results doing A/C work on vehicles in the past but I've never done any work to this F250. I haven't even looked where the low & high side valves are to hook into. When I find them, should the R134 can be turned right side up or upside down to do the charge?

I know these questions are very general but it's just been a long time since I've visited this site and been helped. It will all come back to me with some pointers. Thanks in advance for your information.

Also, with a good performing system with full charge in 75-80F whether, what low & high side pressure should I expect in general?

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It takes all kinds of people in this world, just less of some than others.

Edited: Fri March 21, 2014 at 5:24 PM by BIG

TRB on Fri March 21, 2014 6:19 PM

System takes 2.38 pounds of R134a refrigerant. No specific pressure listed.

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Cussboy on Fri March 21, 2014 7:42 PM

Quote
Originally posted by: BIG
The compressor isn't cycling at all so the system appears to be low on refrigerant. I've owned the truck for 3 years and the A/C has been perfect but apparently has a very slow leak and is low enough the switch has the compressor cut out.

Given the system has always worked perfectly, I really suspect a very small leak.

If the leak was small, you'd still feel some cooling, and the compressor would be coming on. I think you mean by "cut out" that the compressor is not engaging, so that sounds like a larger leak to me. If it was the first case, I might say "add a can of R134a (but WITHOUT ANY sealer)", but since it's low enough to not engage, I think you should measure static pressure to see if there's sufficient R134a in there to engage the system (likely not) and find/fix the leak.

So I'm recommending to take to a dedicated auto AC shop.

Dougflas on Fri March 21, 2014 7:57 PM

Hook up your gauges. Make sure you have a positive pressure. That will tell you that you do not have to pull a vacuum. The way i charge a partially charged system is to put in refrigerant and when both input and exit pipes of the evaporator are cold. I add a couple more oz. This is for orfice tube systems. !500 rpm, doors/windows open, Iusually put a 20 inch box fan in front of the grill; you're looking for 30psi to 35psi low side. High side 225 to 250ish.

BIG on Fri March 21, 2014 10:50 PM

Douglas if I remember correctly whether the freon is put in as a gas (can upright) or a liquid (can upside down) depends on the location of the low side port in the system. Can you clarify for this specific system or at least explain in general so I know how to position the freon can when charging?

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It takes all kinds of people in this world, just less of some than others.

wptski on Sat March 22, 2014 8:54 AM

Quote
Originally posted by: BIG
Douglas if I remember correctly whether the freon is put in as a gas (can upright) or a liquid (can upside down) depends on the location of the low side port in the system. Can you clarify for this specific system or at least explain in general so I know how to position the freon can when charging?
Most vehicles have a high and low side ports which are different sizes. The R134A kits purchased at a auto parts store will "only" have a low side adapter that's insure that you can't connect to the high side with the engine running which could blow the can up. You can damage your compressor if you charge as a liquid on the low side. There are some companies that have YouTube videos calling for some shaking of the can which would cause some refrigerant to go in as a liquid. Don't know if that'll hurt or not.

You can put the can into a bucket warm water no higher than 125F to speed up charging as a gas.

If you have a gauge manifold and the proper high side adapters, it's possible to charge as a liquid with the engine "not" running till the pressure in the can/system equalize. Just have to be "darn" sure that you close the high side manifold before starting the engine and finish the charging as a gas.



Edited: Sat March 22, 2014 at 8:57 AM by wptski

Leggie on Sat March 22, 2014 10:45 AM

Quote
Originally posted by: BIG
Douglas if I remember correctly whether the freon is put in as a gas (can upright) or a liquid (can upside down) depends on the location of the low side port in the system. Can you clarify for this specific system or at least explain in general so I know how to position the freon can when charging?

There are a few types of DIY charge cans. Plain 134a and different types of additive/oil. You can use any kind and charge upright and selectively add 134a. You'll have to add it upside down if you want to the additives to go in as well, but be mindful about adding it slow when you're adding it as liquid so you don't hydrolock the compressor. I'd use the kind that's pre-mixed with the same type of oil specified for your system. Oil is usually lost along with refrigerant at the point of leaks and if you keep topping off just the refrigerant, you can become low on oil and destroy the compressor completely.

Never sealant in any case!

BIG on Sat March 22, 2014 11:08 AM

Thanks guys. I understand. I'll use my gauges hooked to both high and low side, charge with the can upright so no liquid enters the system.

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It takes all kinds of people in this world, just less of some than others.

BIG on Mon March 31, 2014 8:11 AM

I hooked up my gauges and I had 0 static pressure in my system. This changed my mind about simply adding freon to the system as is. I assume my steps now should be:
1) Pull a vacuum on the system;
2) After a full vacuum is pulled through my system and gauges, "blind" the vacuum off and let it sit for as long as it will hold (hopefully several hours or even overnight) to give some idea of how "bad" the leak is;
3) Repair leak - this is assuming the leak is really fast. I assume if the leak is extremely slow and/or difficult to find, as long as I've pulled a good vacuum I can charge the system and move on. The only sacrifice is if the leak is substantial and I charge the system it likely won't stay charged long and I'll be right back where I started.
I need pointers on finding the leak. How is this done? Where in the heck do you start?
4) Assuming the leak is repaired or not, after pulling the vacuum do I need to add the full recommended amount of oil to the system (PAG 46) or not? If so, is it fine to do it through a can and the gages or do I need to remove the compressor and pour some or all of it directly into the compressor?\
5) Complete charging the system after the oil is added.

Please give directions on the steps above that I believe I need to take. I appreciate any feedback.

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It takes all kinds of people in this world, just less of some than others.

mk378 on Mon March 31, 2014 10:54 AM

Zero pressure you typically have an obvious hole in something. A vacuum test is pointless at this point; you know that she leaks. Test with positive pressure. Inert gas can be used if you have it or use small amounts of 134a.

BIG on Tue April 01, 2014 7:59 AM

I know I have a leak but, based on it's performance toward the end, I think the leak isn't a relatively large "hole" but a slow leak. I say this because, at the end of last summer, it's performance wasn't what it typically is. It didn't cool quite as well. Most of the summer prior to that it was ice cold and acted like a new system. Over the winter I didn't use the truck much but, when I did, the defrost didn't work as well as it normally does. Now that's it's time for the a/c again, it won't come on at all and I have 0 static pressure. I just believe it leaked out slowly but, regardless I do have a leak. But, given it's gradual decline, using postive pressure alone to hear a hissing sound through a leak is very unlikely especially given this is a diesel truck where you can't even hear anything over the noise of the diesel engine.

I'm still at a loss as to the best way to locate me leak to repair. Are my steps listed in my previous email a good direction?

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It takes all kinds of people in this world, just less of some than others.

wptski on Tue April 01, 2014 8:19 AM

The A/C compressor won't cycle ON during defrost unless it's in the high thirties or above.

mk378 on Tue April 01, 2014 9:17 AM

The thing about leaks is they almost always get worse over time, not better.

You would do a static pressure test-- no need for the engine to be running. Put in a couple oz of 134a to get the pressure to about 50 psi and see how long that holds. Just open the valves and the gas will go in. Do not try to run the compressor with only this small charge. If the leak spot isn't immediately obvious, go over the system with an electronic leak detector.

Edited: Tue April 01, 2014 at 9:19 AM by mk378