Help! Trying to diagnose AC issues

I've been having intermittent underperforming ac for a few months now. Doesn't blow very cold and sometimes won't cool at all, but sometimes it works normal.
When acting up, both the front and rear show the same symptom.
Checked my refrigerant pressures, at 96 ambient, vent blowing at 70, was about 30psi low and 150 psi high.
To me that high side seems extremely low. Another observation, when I removed the high port dust cap, it had some pressure under it.
I want to try and charge a can or two of r1234yf and see if it improves performance but I'm hesitant because I don't want to overcharge it.

Does anybody have some pointers?

If you buy the parts store AC charge cans, its FULL of sealant and that will eventually plug up ll the small orfaces and make it a future nightmare. fyi...

Deadman said:

If you buy the parts store AC charge cans, its FULL of sealant and that will eventually plug up ll the small orfaces and make it a future nightmare. fyi...

Click to expand...

I'm definitely going to use pure r1234yf with no stop leak additives. It's available at my flaps.

150 psi is generally for 112 ambient but many factors may be in play.
150/30 is out of balance. Both low would be low coolant but when the high and low are out of balance its either

- High too high and low to low = TXV (expansion valve) or orifice tube blocked or restricted.
- High too low and low too high = TXV stuck open or not sealing

I would venture to say your expansion valve or the tube is blocked. Also with 30 psi low you are near the freezing point so if the day is humid your coil could be freezing up hence the intermittent cooling.

Marshy said:

I've been having intermittent underperforming ac for a few months now. Doesn't blow very cold and sometimes won't cool at all, but sometimes it works normal.
When acting up, both the front and rear show the same symptom.
Checked my refrigerant pressures, at 96 ambient, vent blowing at 70, was about 30psi low and 150 psi high.
To me that high side seems extremely low. Another observation, when I removed the high port dust cap, it had some pressure under it.
I want to try and charge a can or two of r1234yf and see if it improves performance but I'm hesitant because I don't want to overcharge it.

Does anybody have some pointers?

Click to expand...

Do you have a 2018? If so, there was a TSB about some type of AC contamination from the factory.

Both pressures seem low for a R1234yf system. More like 60 on the low and 175-200 on the high is normal when the system just starts to cool off a hot car at that ambient temp assuming humidity is also high. If you got a burst of pressure taking the cap off then for sure the Schrader valve is leaking and might be the entire problem of why it’s low. I did see some stores selling pure cans and no sealant R1234yf. Maybe buy a kit to top it off through the low side then with the cap off fill the valve with water. If you see any bubbles, it’s for sure leaking. This stuff below is also helpful to find leaks,

Big Blu Subzero Micro Leak Detector 1Qt https://a.co/d/37cR0Dp

Your symptoms sounds like my 2019 Expy. Took to Ford dealership 4 times over the course of 3 summers (4th time being right now and they still have it - been there since last Monday) and they are finally replacing the compressor and evaporator all under warranty. Should be ready this week. If you are still under warranty, take it in.

Update...so I charged my system with about 12 oz of r1234yf using the honeywell service cans. The system began to cool normally again and has worked normally for a couple of weeks.
I guess I have diagnosed a slow leak. Let the games begin...

Marshy said:

Update...so I charged my system with about 12 oz of r1234yf using the honeywell service cans. The system began to cool normally again and has worked normally for a couple of weeks.
I guess I have diagnosed a slow leak. Let the games begin...

Click to expand...

My 2019 had a similar occurrence. I also added a can of R1233yf and it seems to have taken care of the issue. The vents are now blowing in the 20° to 30° range when set to max. I only had a low side gauge. It started at 25 psi and the 8 oz can took it to 35 psi. My ambient was about 85°F.

Has it happened again or did you find the leak?

The rear AC unit has been the culprit in many cases. If you didn’t use UV dye, get a refrigerant sniffer.