ac is charged, won't blow cold air?

[outracing]

So as I stated, my AC system is charged, the line and accumulator is cold to the touch. The pump engages and runs fine. With the exception on one or two bugs, the condenser is clean and the fins are in good shape. What would cause my system to give me no cold air?

 

[ehall]

broken blend door?

 

[outracing]

The blend door operates just fine.

 

[Shorty]

is the low side line cold?

is the high side line hot?

does the compressor cycle more than once per minute?

 

[Boss Cherokee]

No offense intended but where do we start to attempt to answer you? Were you working on the system? It seems yes because you stated a new line and accumulator was cold! If so did you pump it down and hold it for leaks? Did you replace the line filter? Did you keep the suction and start to charge it with the suction? If not you do not have enough freon in the system or you may have too much! Start over pump it down! You can use a hermetic compressor off an old fridge. Get a freon/ a/c valve with a compression style fitting from your local supply house. If you have a/c gauges hook them up if not Harbor Freight has cheap ones on sale and as much as you will use it they'll last your life time! That hermetic compressor will pump it down way past 8 pounds of vacuum so keep an eye on it.

 

[outracing]

Low side is very cold
High side is definitely hot
Compressor cycles in about 15-20 second intervals.

I am banging my head here, I just don't get it. Today it was only 76 degrees out, the coldest I could get the air to blow out was 64. It kinda warm up as I drive as well, by then end of my 15 minute drive, I was getting 69 degrees.

 

[ehall]

line is clogged?

 

[outracing]

Ehall, what line should I inspect?

 

[Digger87xj]

take readings at idle, fan on high, recirc mode, windows open. The clutch should not cycle, and the gauge should read 35 psi.

Is the efan running when the clutch is on?

15-20 seconds is to rapid. either the evaporator is too cold from low blower speed or there is not enough freon charge, or head pressure is too high (e-fan not running)

 

[outracing]

Digger, I am reading about 42 wth the windows open recirc on and max blower. The electric fan kicks on everytime the clutch engages. When the clutch kicks off it jumps up to about 55.why should the cluch not cycle at idle? I still want to be cool when I am sitting behind the school bus...

 

[Overland]

Low side gauge doesn't show differential. You need a manifold to see it. You also need a vacuum pump, which I'm assuming you don't have, as you're displaying a low side gauge.

I think you could have some moisture. It freezes at the expansion orifice and clogs the line. Accumulator and expansion valve are cheap, you can borrow the manifold and pump from the parts store.

Then you say it reads 42°, does it blow cold or not?

 

[Digger87xj]

So tell me where this began...? Are you attempting to charge an empty system? Or adding to a system you assumed low?

 

[outracing]

Overland, the air that blows out is always 55-60 degrees. 42 & 55 is what the gauge reads on the low side. I'll talk to the guys at AutoZone and see what they have on their loaner tool program.

Digger, neither. I just bought this Jeep a bit ago. I just noticed that the AC isn't working correct now that the weather is hot. I have the gauge for the low did left from when I refilled an old vehicle. Just figured I'd see what kind of pressure I had.

 

[FG Jeep]

I work on ac pretty regularly. From what you are describing sounds like the compressor is short cycling. This is normally caused by low refrigerant charge.

A few things about refrigerant. I assume that this is a r134a system. R12 follows the similarbguidelines but there are a few differences. I'm going to address r134a here.

First off the condenser e fan should come on when the compressor is clutch is engaged.

General normal low side pressure is 35-40psi.

General high side pressure is around 200-250 depending on the ambient temp. Even 175 is ok if it is a cooler day out and the system isn't working to hard.

R134a really needs the correct charge. To little and it will short cycle and not cool. To much and the system will not cool correctly. The cans from autozone with the red, yellow, and green gauge on them only get you in the neighborhood of a correct charge. R134a is charged by weight. You really need to charges it with a machine in most cases to get a accurate charge.

At home charging is done on the low side with the air running while the engine is running. With a ac machine you can charges on the high side with the engine off or both sides at the same time with the engine off.

If the system is open for a repair it needs to be put into a heavy vacuum (29 in/hg) for 15 minutes to boil any moisture off. Water boils at about 60 degrees Fahrenheit at 29-30 in/hg. Having moisture in the system will effect the cooling out put.

When the compressor clutch is disengaged the high and low side pressures should equalize normally around 80 or so psi when charged. That means the moment the system cycles off the pressures will try to equalize. If the compressor is short cycling it will never maintain proper pressures.

If your high side pressure goes high (low side should stay high as well)and the cooling becomes poor. Normally this is from poor airflow through the condenser. Look for the Efan to not engage.

The situation described above sounds like a low refrigerant short cycling situation. More than likely cause by a small leak. This is probably the most common ac problem I run into. The best way to try and find the leak is look for oily spot. Pag oil is a bit sticky. If your unable to locate a oil spot. Evacuate the system. Put the system into a light vacuum. Vacuum it for a few minutes, put some dye in and fully charge it. Then drive around using it for a week or so and check with a black light. Most small leaks take a good week or so of use to actually show themselves. Sometimes longer. Generally we don't ever add to the system. We recover add dye and recharge. You never know how much is in the system and because it is charged by weight and needs to be accurate this is the easiest preferred method. Granted you can watch the pressures and get it pretty darn close via system operating pressures.

Never buy refrigerant with stop leak in it. All it does is mess stuff up. Fix the leak properly don't band aid it.

If you want to become 48 state certified for r12 & r134a take the epa 609 test. It's about $35. If you want all 50. Wisconsin and California have different regulations take the epa 610 test. It is also about $35. The study guide for the test explains how the system works and how to trouble shoot. All the ac system is a giant heat exchanger.

Hope this info helps you figure out what is going on.

 

[Digger87xj]

It's possible there is air in the system as well. If someone took it apart and recharged it without first putting a vacuum on the system, it will show the readings you are getting. 42 psi is high IMPO, and if you add more freon it will just get higher.
I think your best bet is to take it somewhere and have an evac and refill done. This way the system can be checked for leaks, air and moisture expelled and the the system will get the proper charge.

Or, get a DIY can and add a little freon at a time and see what shakes out.

 

[md21722]

If you don't have the right tools, I think its best to invest in the tools, or take it to a shop.

If you don't do this type of work frequently, it may be best to pay a shop, but don't pay anyone who says "old system, change everything".

Every A/C shop will pull vacuum and hold it on the system before recharging. If the vacuum drops while holding, there is a leak, moisture, or both. Pulling vacuum removes the air and boils out the moisture. Neither should be in your A/C system.