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AC not ice cold anymore but pressures look ok

DrkPony

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City, State
Delaware County, PA
Year, Model & Trim Level
2004 Mounty Premier AWD
My AC used to be so cold I could never have it on full blast. This year its just cool air blowing and when it hit 90 out it was a little too uncomfortable in the car. Thermometer in AC vent showed about 55-60 degrees, when it was 80 out. Checked pressures its about 32 low and 172 high, I added 12oz R134a but pressures only went up a few psi (+2 low, +5 high). Air feels a little cooler, but not like it used to be. I know capacity is 32oz, but I don't want to overcharge when the pressures already look ok. I would have expected a bigger jump in psi due to 12oz. Recirculator is working fine, I checked it. What else could it be? air in the system? It's a 2004 and AC has never been touched before.
 

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If its never been opened and has always had pressure then I would rule air in the system out of the picture.

My first point of inspection would be the Orifice Tube. Compressor plates could be beginning to break up and you may find a bunch of little metal flakes clogging the screen on the tube.
 






Before you start digging make sure all of the simple stuff is checked out. Damper doors etc.
 






If everything is found to appear normal, or acceptable, look at the mileage on the compressor. If very old, compressors DO wear out; their "volumetric efficiency" drops, resulting in less and less efficient pumping action. Very often, a well-worn compressor will still maintain acceptable system pressures, but just doesn't pump enough gas. imp
 






112K so about time something goes bad (besides bearings and ball joints). I never used to hit the recirculator button, but now i do since it drops temp from 65 to 55-60 at vent. I might just hold out another season and then make an attempt to rebuild the system.
 






A "worn out" compressor or orifice tube problem would show up on the gauges. Bad compressors don't make good pressure. If your compressor isn't moving "enough" you will show static pressure.

Adding more r134 will raise your STATIC pressures, not dynamic. That depends more on latent heat.

Your post isn't clear. Were pressures at 90 degrees or 80? Was this the ambient temp?

How did you take the pressures? Was the engine ran at 1500 rpm for 5-10 minutes? Was the fan on high and ac on recirc? Was the vehicle in the shade? Was there a shop fan in front of the condenser? You must do all of these to get an accurate pressure. You can omit the fan if you don't have one.

Did the system cycle the clutch when the low side hit 20-25 psi? Did it ever cycle?

If you really did lose a pound of r134 then you are also low on oil by about an ounce or two. Did you put in virgin r134? Did it have oil or UV dye added?

Suction pressure directly correlates to evap temp. If your suction is 30s/40s on a 90 degree day then you should have cold air. Something else is wrong like blend door etc. High side should be around 2.2 times the ambient temp. (ambient means temp in the shade under a tree)

If you have a leak then the next can you use should have UV dye in it. Although, I'm willing to bet you can find a wet spot of pag oil at the leaking junction/hose.
 






We don't have plates or suction valves, we have scrolls ;)

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It was 80 out partly cloudy, fan high, recir on, no outside fan. The engine was running for 10 minutes but not with a fast idle, is there another way to do this on the electronic throttle body without sitting in the car with my foot on gas?

Today was 80 and cloudy out, I was idling for a while and it hit 45 at the vent, after I drove away the temps went up to 55-65 at the vent. I dont think I hear the clutch cycle like I used to, but I'll take a closer look in a few days when I get a chance.
 






A "worn out" compressor or orifice tube problem would show up on the gauges. Bad compressors don't make good pressure. If your compressor isn't moving "enough" you will show static pressure.
.

In what way? Smaller "spread" between low and high side? I find some of your statements misleading.

Do you mean to imply that a working compressor MUST move adequate volume? Mostly true working with incompressible fluid, as in hydraulics, but Freon compressors move gas. Efficiency dictates that high-side pressure MUST be adequate to liquefy the refrigerant as heat is removed in the condenser, no? imp
 






"We don't have plates or suction valves, we have scrolls."

Are the scrolls made of metal?

I am just referencing what I have seen over the past 30 years.

I'm no engineer, no expert, just and old field technical service hand and I have seen a lot of weird stuff.

I've even seen receiver \ dryer desiccant internals burst and spread dust throughout the system. The O tube screen catches it.

Your actually boiling liquid Freon in the evaporator. For efficient heat transfer in the evaporator a certain level needs to be maintained. Pressures may look good but if you can't keep the level right thermal transfer will be inefficient.
 






DrK Pony,

Quick check you can do.

Is the low side line going to the receiver \ dryer "Sweating" or real cold to the touch after the system has been running for a while?

If it is, my opinion is that the system is working correctly and your getting "excess heat" from somewhere else.

When I charge a system I use gauges, but also watch the suction line. Once it starts sweating I usually stop adding gas.
 






I took the mounty for a road trip, it's 90 out and working well 50 at vent with fan on low. Earlier at gas station it was 70 out, popped the hood and found just a little ice on dryer.
 






Seems like the system itself is cooling properly if you have ice built up outside on the lines.

I have a 98, but don't the later models have a Cabin Air Filter?

Could that be clogged?

Restricted airflow would be just like your home A\C. Loss of cooling.
 


















No worries
 






I took the mounty for a road trip, it's 90 out and working well 50 at vent with fan on low. Earlier at gas station it was 70 out, popped the hood and found just a little ice on dryer.

That's perfect! :thumbsup: 40-50 out of the vent on low during a 90 degree day is the exact spec ford cites for proper operation.

Now, let's address the warming up on the highway. Are the vent temps still colder at idle?

It's possible that the clutch is being rapidly cycled at higher rpm due to the low pressure side going too low. This can be caused by restrictions, like dessicant or 'black death' clogging the orifice, as mentioned by

I've even seen receiver \ dryer desiccant internals burst and spread dust throughout the system. The O tube screen catches it.

He could totally be right.

Or simply from the system being low on charge. Paradoxically, overcharge can do the same thing, as the high pressure cutoff engages and disengages.

Overcharge can hurt performance exactly like low charge. This is why those cans from Autozone with only a low side gauge are dangerous. You need to see the high side, too. Otherwise one might think they're still low until they're compressor grenades.

This is where the pressure reading at 1500 rpm for 5-10 minutes becomes important. It simulates pressures and cycling behavior like you're cruising along at 60 or whatever.

I don't know how to trick the throttle by wire system, so you'll have to find an assistant.

Repeat your test, in the shade, recirc max ac, fan on low, have your assistant keep the engine around 1500. It will take 5 minutes at least to stabilize the behavior.

After that start watching the gauges and try to see what's happening. Is it cycling because the low side is getting pulled down into low 20s? Is the low side actually going into vacuum? (This will happen from the orifice tube screen being partially clogged as mentioned by the other poster.)

Or is the high side skyrocketing?

This will help you determine possible over/under charge and/or loose desiccant or contamination.

These systems, especially the systems with aux (rear) ac, are super sensitive to charge. Once you get a leak, you lose track of how much charge is in the system. Especially since most cans for DIY use have a few ounces of oil, dye, or stopleak in them, which takes up volume in the system.

It's best to the fix any leaks, vacuum the system, and fill by weight.

But I think the gauges will give us a pretty good idea.

I slowly titrated my system up by 2oz at a time until I found the mix of good idle and highway cooling performance + proper low and high pressures. (Be careful to purge your gauges of air before doing something like that as the volume of air in the hoses can start to add up.)
 






Also check your fresh air door. I work for ford and have done many of these. If you pop out the blower fan and look up you can see if. They like to brake and fall off.

Yep. I did the "mod" to mine a while back. (ripping it out :D )
 






"We don't have plates or suction valves, we have scrolls."

Are the scrolls made of metal?

Teflon coated metal if I remember correctly.
 



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