Auto AC Question

Okay, YES I know to do it right Id need a set of gauges for High and Low pressure butttttttttt all I have is one of those cheap 134A can type filler gauges between the 12 oz can and the low pressure suction fill side.

Soooooo the Chevy RV has a slow freon leak and needs charged maybe once a year. A while back it began short cycling the compressor with not too cold air and finally it got so low it quit even cycling. Sooooooooooo I toss in one 12 oz can and it starts short cycling maybe cooling just a bit Sooooooooo then I add another 12 oz and it starts to get pretty cold buttttttttttttttt at idle it still cycles somewhat albeit she pumps a fairly long time and is blowing cold air. The cheapie low suction side gauge shows good/safe green 25 to 55 and when shes pumping it drops to around 35 and when she cycles off it rises to maybe 40 to 45.



QUESTION 1 Think it needs one more 12 oz can???? Cuz why does it still cycle (but runs fairly long and air is cold) at idle????

QUESTION 2 Using those 12 oz cans will she not take anymore then she needs??? i.e. if another 12 oz can is too much will it simply not take it all???? I KNOW TO STOP IF SHE GOES OUT OF THE SAFE GREEN 55 AND STARTS INTO THE RED HIGH DANGER ZONE but with the 2 cans I added shes still safely in the green so far.

Thanks in advance, its hotter n a hammered "Hill" and were takin the RV to Evansville and Louisville to see the sons band play the next couple nights AND I WANT IT COOL WHILE DRIVING.

Ol John T and all

sounds like the thermostat is kicking out...make sure you got everything on max and leave the door open...if it still cycles it may need a bit OR you've overfilled it and high pressure cutout on high side kicking off.

It is just me, but if it quit alltogether because of low freon, I would add one more can to see if it helps. If not, the thermostat in the evaporator could be bad. Stick a thermometer in the air outlet and check temp.

As you MAY be aware, typically modern auto AC systems use a low side pressure switch (rather than a thermostat) to cycle the compressor.

Do you have a temp probe you can stick in the dash vent? Air outlet temps in the low 40's is as good as it gets. I wouldn't add any more just yet. Ambient air temp directly affects cycle time. If it cuts out about 30 psi and back in about 40, that sounds about right. Put your hand on the low side hose close to the compressor. If it's good and cold with the fan on high, don't add anymore.
Adding oil would be a good idea. If you add any more, start with an oil charge.

I would feel better about adding another can if I checked the high side pressure first and determined it was an appropriate condensing pressure for the ambient temp.

The ambient temp is like in the 90's is one reason why I've decided to hold off on another can until I drive it tomorrow in the hot temps n see just what she does. It is cooling pretty well and the low side is in the safe green range so I better hold off until a try it while driving tomorrow, I can always add a can Wed night but feel like 2 ought to be enough especially since she stopped short cycling and cooled slightly after one can. I just dont like that cycling while idling (although it pumps failrly long before a short drop out) now butttttttttt if you figure its 90 outside and she is cooling I think I will wait n see how she does on the road tomorrow

Thanks, John T

The sight glass will tell you when it's full.It goes from cloudy to clear when the system is full.

R134 requires exact amount of refrigerant to work properly,so it is best to evacuate and put in exact amount for vehicle.
Does not top of well like the R12 did.

R-134 does NOT typically present a clear sight class when fully charged like R-12 did (leading to an overcharge and broken parts if you try put enough refrigerant in the system to try to clear it up), PLUS most newer systems do NOT even have one.


---Bob (EPA section 608 and 609 certified.)

Heck John,

I've been using nothin' but those fill hoses since forever; you don't need all the goody two shoes expensive equipment.

Hold your hand on that receiver; if it's too cold to comfortably hold, you're full.

If that compressor locks up, you're overfilled. :>)

Allan

Most modern vehicles with a single evaporator typically only hold about 24 ounces total. I hear newer vehicles hold even less. Over charging is bad, bad, bad.

Bingo.

I always evacuate and recharge with the proper amount.

If you do not have a vacuum pump you can most likely rent one from a tool rental store.

Dean

You SHOULD have a decal that tells how much refrigerant your system holds. That being said, if your compressor quits because of too low pressure, it's safe to figure that it is empty. Since you have a larger vehicle, it may well hold more than 24 ounces; check for that decal. There is a reciever/dryer in the system that can hold at least 8 ounces of extra refirgerant; new 134 mixes just fine with 'old' 134. It's the so-called 'blends' like Freeze 12 that don't mix and must be evacuated if overfilled.

That's why we STOP adding gas JUST BEFORE it locks up, RIGHT, Allan?

"It's the so-called 'blends' like Freeze 12 that don't mix and must be evacuated if overfilled."

ANOTHER "old mechanic's wives' tale, (NOT that mixing them is PROPER.)


Actually, Freeze-12 IS 80% R-134, with 20% HCFC-
142b added to help the old mineral oil circulate in the system!

Don't believe me, look up Freeze-12 in the EPA chart at the link below:http://www.epa.gov/ozone/snap/refrigerants/macssubs.html

It should cycle a an idle. Go by the presure on the low side. Presure will change with outside air temp. The cheap ac set does"t account for that in the green zone. Some times the alert portions of the gauge is where it needs to be. It all depends on outside air tems.

What year and is it a class A or class C?

well,if its after '88 i'm not aware of any changes since i retired from FOMOCO dealerships.
Ford was still using high and low side switches plus a t-stat last i recall.

John T;
Sounds low to me too. 1 - It shoulden't cycle when on max. 2 - Yes you can overcharge it with those 12 ounce can's just not as quick as with a jug. You can add just enough to stop it from cycling and you will be close. Too much and it won't cool good & it will kick out on hp.

I don't like topping off vehicles but I do it once in a while. Most times I pull a vaccume & weigh it in. Course I already have all the equipment so it's no biggie. Have fun on the road trip.

Put the control on max cool, have someone sit inside and rev the engine up to regular operating rpm. If it is still cycling on and off it probably needs a little more refrigerant.

At idle the air may not be as cool. the compressor does not pump as fast at idle, pressure comes up a little.

If it cold then it might be good to stop there.
take your hose and some extra cans along on the trip and add if needed.

If you set the freon can in a can of hot water then it will get sucked in WAY faster.

One thing my ac man taught me was to spray water through the condenser at idle. See if that makes it cooler and changes the cycling.