134a high side pressure over 300

[i6pwr]

Wanted to start a new thread regarding our 2015 Impala 3.6 V6 in case others have this issue, I started with how much oil needed but looks like it might be more than an evac and recharge. The AC recently has taken a long time to cool down from sitting in the sun for hours, and never really felt very cold. I put some gauges on it and with the ambient at about 79 deg, I have 80 psi static in the system, When I start it up and let it run for about 5 min, I have 37 psi on the low side, and 315 psi on the high...with around 62-63 deg at the vents...lowest temp setting, fan on high, no recirc. The needles will move to about 52/255 before the compressor kicks in again....or whatever it does as it doesn't appear to be a front clutch style compressor.

Does this point to a restriction or something else? If an expansion valve issue, where is it located on this vehicle? The condenser has some dings so maybe the dryer bag is the culprit, but thinking of replacing the condenser due to it's age and number of dents. I put some dye into the system but don't see any traces of the dye. Curious to where to start looking if these pressures are too high,

 

[JTK]

Is the cooling fan running at full speed when the high side hits 300+ psig?

 

[i6pwr]

Is the cooling fan running at full speed when the high side hits 300+

The fan is moving a good amount of air, sounds loud enough to make me believe it is but I don't mind verifying that as I'm not 100% I can check RPM or voltage or both.

 

[brages]

If you shut off the car, how long does it take to equalize to 80 psi both sides?

Is there only one fan? I would be thinking fan myself.

 

[Eddie Hudson]

INTERPRETING PRESSURE READINGS​
Low-Pressure Gauge	High-Pressure Gauge	Action Required
IN RANGE	IN RANGE	A/C is working properly.
LOW	LOW	Add Refrigerant.
LOW	HIGH	Need service, possible blockage of the expansion valve or orifice tube.
HIGH	LOW	Needs service, possibly faulty compressor.
HIGH	HIGH	System is overcharged Slowly remove refrigerant. Venting is illegal in USA.

 

[i6pwr]

If you shut off the car, how long does it take to equalize to 80 psi both sides?

Is there only one fan? I would be thinking fan myself.

I didn't check the return to static pressure time, but will try today or tomorrow. Pretty sure there are 2 fans.

 

[shortyb]

If it turns out to be the expansion valve, you might get lucky and it's on the engine side of the firewall where A/C lines go inside the car. Otherwise, it may be attached closer to the evaporator and the dash has to come apart. Not fun.

 

[i6pwr]

Otherwise, it may be attached closer to the evaporator and the dash has to come apart. Not fun

Yeah, I saw that. The evaporator job looks like a nightmare. I believe the expansion valve is located at the firewall connector, but not 100%.

 

[mk378]

Have you added oil? Too much oil is bad it will prevent the condenser from working properly.

 

[i6pwr]

Have you added oil? Too much oil is bad it will prevent the condenser from working properly.

No, was going to evac and recharge but noticed the high pressure and wanted to ask around first.

Just checked the AC, ambient is 73 deg, at idle I have this with 43 deg at vents.

LH fan is running at around 1590 RPM and RH fan is around 1140 RPM, not much load and as of now it seems OK. When it gets hot outside all that changes quick. Above 80 deg the cooling is poor.

If you shut off the car, how long does it take to equalize to 80 psi both sides?

Revisiting your question....


This is about 3 min after I shut the engine off and the needles are barely moving during rest. Will give it about an hour and check periodically.

 

[i6pwr]

So far this is what I have at 73 deg ambient.

Idle: 32/170 PSI
At shutdown: 42/140 PSI
30 min after shutdown: 77/90 PSI

 

[shortyb]

That big of a pressure increase on the high side with minimal increase of ambient (73F vs. 79F) with increase of temp at vents (43F vs. 62F) points me to a bad/failing expansion valve. But thats just me.

 

[i6pwr]

That big of a pressure increase on the high side with minimal increase of ambient (73F vs. 79F) with increase of temp at vents (43F vs. 62F) points me to a bad/failing expansion valve. But thats just me.

I forgot to add, tonight during testing, at approx 1800 RPM @ 73 deg ambient, I had 22/205 PSI, meant to add the raised RPM pressures earlier. The 325 PSI I had before at 80 deg ambient was also at 1800 RPM, and around 275 PSI At idle.

 

[i6pwr]

I trust (hope) this is where the expansion valve is located, where the lines enter the firewall. If it comes to this, and is accessible from the outside.

 

[shortyb]

I trust (hope) this is where the expansion valve is located, where the lines enter the firewall. If it comes to this, and is accessible from the outside.

View attachment 298565

Hopefully so and not just the connection between outside/inside components. Thats sort of what my VW looked like when I replaced the TXV recently, however, you can actually see the valve on the other side of this connector. Good luck.

 

[i6pwr]

however, you can actually see the valve on the other side of this connector

Looks to be the same, but never researched this so could be visible from the outside with a "come and try to get me" look on its face...lol.

 

[i6pwr]

It took just under an hour for the pressures to equalize after shutting the engine/AC off.

 

[brages]

It took just under an hour for the pressures to equalize after shutting the engine/AC off.

From what I've seen on Youtube, that seems like longer than it should take, maybe the expansion valve is bad. Sure looks like it's right there on the firewall.

 

[JDenyer232]

Here's a quick test to try. Run the the ac on max with the windows open on a warm day. Hook your gauges up. Let things stabilize. Now spray your condenser with water from a garden hose. If the high side pressure drops quickly then I would suspect a clogged condenser or fan not turning fast enough. If the high side pressure doesn't drop quickly then I would suspect a plugged expansion valve. The plug in the expansion valve could be sludge or even frozen water if the system has been opened up and not evacuated properly and a new dryer installed. A restricted expansion valve usually does not result in high head pressure though. Think of it this way, the condenser is large enough to hold the entire charge in it's liquid state. If there is a restriction then the refrigerant is held longer in the condenser giving up more heat. Temperature and pressure being tied to each other results in lower pressure not higher pressure. The low side pressure will be lower than normal though. I know it sounds counterintuitive, but think of it this way. The restriction slows the refrigerant flow thru the entire system, more liquid stacks up in the condenser and has more time to give up heat, thus the pressure does not increase and may even decrease. There are 2 things that will drive the high pressure way up. One is a condenser that is plugged up on the outside. The other is air in the system. The most common way for air to get in is thru your hoses. If you don't purge your hoses each time you hook them up you will suck air into the system. Let's say the ac is off. You hook up your hoses and if not purged with refrigerant there is air in them. The gauge reads say 55psi. Now you turn the ac on and the pressure starts to decrease. The higher pressure air in the hose will flow toward the system that is now at a lower pressure. High pressure always flows to low pressure. Now you have air in the system and air can't condense, it just takes up space and increases the head pressure. Each time you hook up hose that are not purged you suck in more air. I really think that you have either a dirty condenser, or air in the system. If it were me I would clean the condenser first then recheck purging the hoses first of course. If that didn't improve things then I would recover the charge, evacuate with the vacuum pump, and weigh a fresh charge in. The pressure may take a long time to equalize with the ac off if the thermostatic expansion valve doesn't have a equalizer line which most cars do not. Sorry this was so long, but I really hope this helps.

 

[i6pwr]

Here's a quick test to try. Run the the ac on max with the windows open on a warm day. Hook your gauges up. Let things stabilize. Now spray your condenser with water from a garden hose. If the high side pressure drops quickly then I would suspect a clogged condenser or fan not turning fast enough

Was able to do this as well as ensure the charge was correct. I had the system evacuated since there have been multiple gauge connections and the previous service was done before we bought it and I wanted to be sure there wasn't any extra air, oil, etc.

With te fresh recharge I was getting 42 deg at the vents with 70 deg ambient. However that was short lived and while the overall cooling had improved, it still gets warm.

Today we stared it up, 75 deg ambient, and it was blowing warm. I sprayed the condenser and it cooled off inside, I also popped the hood and the fans were not spinning. After I sprayed the condenser, I checked the fans again and they were not spinning fast. Usually as soon as the AC kicks on at least one fan should spin correct?

The fans do spin, but this appears to either be a fan speed issue as suspected or a bad condenser.

I wish I knew the fan speeds as requested by the PCM.