A/C Pressures Wildly Fluctuating

[JakePSD]

I've got a 2017 GT PP. Just under 9k miles. I've had to have the A/C recharged once or twice before due to a refrigerant leak. At first I thought it was the evaporator core considering they had issues, however I noticed yesterday when attempting to recharge it myself that the high side port had a few bubbles in it when I removed the fitting. I mention that just to give everyone here an easy thing to check before assuming it's the evaporator.

Anyway, the real issue I'm having is that both the high and low side pressures are all over the place. With the engine off and the system equalized, the static pressure appears dead on (95-100 degrees ambient, 120 psi +/-5). Once started, A/C on max, engine at idle, low side is about 35-40 psi, high side about 240 psi. Air out of the vents drops to about 58 degrees.

Once I bring the RPMs up is when things go haywire. Around 2500 rpm, the low side drops to about 20 psi and the high side climbs to about 320, which I assume is normal. However, after about 10 seconds the low side and high side start fluctuating. Minimal at first, but continuously getting wider and wider fluctuations until the high side hits the roughly 475 psi cut out, at which point the compressor kicks off until the low side comes back to around 50 psi, then the process starts over. It also acts up at rpms as low as 1000, it just takes longer before it kicks out. It's really only steady at idle.

Anyone have any ideas? I'm thinking maybe a faulty expansion valve, but I'm not sure if these cars have that, or an orifice tube, or even the weird valve system they used on the mid to late 2000s Taurus. Or maybe it could be a faulty sensor throwing things off? I have Auto Engineuity so I can look at all the sensors if I knew what I was looking for.

EDIT: Here is a video of what's going on. It's a bit lengthy (about 16 minutes). Watching the whole thing isn't necessary, it's long because I show what it does at various RPM.

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[K4fxd]

Sounds like there is some trash in the system. I have a 17 did the same thing. I had to replace the condenser and the A/C compressor.

Mine got to the point it would hit the high pressure limit after about 1 second of operation then the pressure would take 30 to 45 min to drop to normal.

 

[JakePSD]

Sounds like there is some trash in the system. I have a 17 did the same thing. I had to replace the condenser and the A/C compressor.

Mine got to the point it would hit the high pressure limit after about 1 second of operation then the pressure would take 30 to 45 min to drop to normal.

Well that's not news I was hoping for haha. What steps did you take to determine that? Where did the trash accumulate? Any idea where the trash came from? I'm hoping that isn't my problem but if it is I'll deal with it. I just don't wanna load the parts cannon and spend hundreds on parts that I don't actually need.

 

[Dana Pants]

You need to keep track of the grams refrigerant. If the system is overcharged or undercharged, weird behavior happens. How many cans did you add? How much refrigerant was in each can? Was the system completely dead?

 

[K4fxd]

I waited till the system did not work then opened it up and founend the condensor clogged. I think it was trash from the compressor or could have been from the dryer. The new condensor came with a new dryer so I didn't trouble shoot any further.

 

[JakePSD]

You need to keep track of the grams refrigerant. If the system is overcharged or undercharged, weird behavior happens. How many cans did you add? How much refrigerant was in each cab? Was the system completely dead?

I'd say I aded at most 6 ounces. It was whatever was left from a can I had from last year (sealed and stored cleanly). The system was not completely dead, just not working worth a crap. I may have overcharged it some, but I ended up recovering some of it back out to try to remedy the problem, obviously to no avail.

 

[JakePSD]

I waited till the system did not work then opened it up and founend the condensor clogged. I think it was trash from the compressor or could have been from the dryer. The new condensor came with a new dryer so I didn't trouble shoot any further.

Gotcha. Must have thought since it's not working you've got nothing to lose? Pretty much where I am haha.

 

[mrgooden]

So does it the AC cool well at idle and while driving? You should also be proving a good flow of air with a large fan if running at 2500 RPM still. Head pressure will increase as RPM increases, without good airflow,the high pressure cutout can certainly be triggered.

Richard

 

[K4fxd]

Gotcha. Must have thought since it's not working you've got nothing to lose?

It was slipping the A/C clutch enough to get smoke from it due to the high pressure in the system. I figured I needed a new clutch so just decided to replace the compressor.

Cry once and all that.

 

[Dana Pants]

It’s breaking my brain that this thread uses English units. 6 oz is 170 grams. It takes about 600 grams to charge the system. I would Probably throw another 200g can at it and see if things get better or worse.

 

[Basspro302]

Usually the dryer bag splits open causing a blockage in the condenser. Could be the expansion valve but usually they stick open or closed .

 

[JakePSD]

It’s breaking my brain that this thread uses English units. 6 oz is 170 grams. It takes about 600 grams to charge the system. I would Probably throw another 200g can at it and see if things get better or worse.

Based on the pressures I'm seeing, adding that much would very much over charge the system. The static and idle speed pressures appear to be pretty spot on. Sorry about the freedom units haha. I actually had more in the system yesterday before I recovered a little bit at a time to get the idle pressures where they should be.

 

[JakePSD]

Usually the dryer bag splits open causing a blockage in the condenser. Could be the expansion valve but usually they stick open or closed .

I'll probably take it to the Mazda dealer the woman works at and evacuate the system and open it up and see if there is trash in the condenser. They will let me use stuff their cheap or free as long as they have an open bay.

 

[mrgooden]

Usually the dryer bag splits open causing a blockage in the condenser. Could be the expansion valve but usually they stick open or closed .

I know most of the expansion valves I've replaced had pin holes in the capillary tube due to rubbing or something similar preventing them from opening. I primarily worked on 130+ LB R-22 systems, had like 8 Expansion valves or so. Do a bit of car AC work if I feel like helping friends out or my stuff. Luckily I could pump majority of refrigerant into the receiver and close off so we didn't have to recover all the refrigerant each time.

Richard

 

[JakePSD]

I know most of the expansion valves I've replaced had pin holes in the capillary tube due to rubbing or something similar preventing them from opening. I primarily worked on 130+ LB R-22 systems, had like 8 Expansion valves or so. Do a bit of car AC work if I feel like helping friends out or my stuff. Luckily I could pump majority of refrigerant into the receiver and close off so we didn't have to recover all the refrigerant each time.

Richard

So based on your experience, is what's happening to me a possible expansion valve problem?

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