Automotive Air Conditioning Information Forum

2013 Sentra AC problem. Compressor turns on but high pressure = low pressure. Ambient temps outside are 88 F.

My high side and low side are both showing 85 PSI. I verified that the clutch is spinning which should mean the compressor is working. I just replaced the compressor also and the symptoms are the same.

It has the correct charge. It is very weird that the compressor is spinning *i can see the clutch spinning* and the pressures are not changing on the high or the low. Also, if i turn the AC off, the pressure stays the same 85 PSI.


A friend told me the try changing the expansion valve but I do not know what to do now... I have experience with ACs, I did a full vacuum and charge with ac oil when I replaced the original compressor yesterday. Everybody online says if the pressures do not change the compressor has failed but this is a second compressor i JUST installed so its not the compressor. Also there are no funny noises.


Any help would be appreciated please. This car only has 60k miles.

richietlc wrote: I verified that the clutch is spinning which should mean the compressor is working. I just replaced the compressor also and the symptoms are the same.

The AC clutch can - and should spin - but it's the engagement part, the CENTER part spinning that's important.

If you weren't getting a pressure differential, how did you get a full charge of refrigerant in ????

Cusser wrote:

richietlc wrote: I verified that the clutch is spinning which should mean the compressor is working. I just replaced the compressor also and the symptoms are the same.

The AC clutch can - and should spin - but it's the engagement part, the CENTER part spinning that's important.

If you weren't getting a pressure differential, how did you get a full charge of refrigerant in ????

Hey thanks for the reply! So, I charged about 10 oz of R134a which is not a full charge but it should be enough for the system to turn on and the pressure to differentiate. Hmm, I am going to look at the center part and let you know later on today if its spinning or not. I had no idea that there was a center part that should be spinning along with the clutch, I thought it was all in sync!


Also there are no leaks in this system. Also, I remember how I charged it initially. After the vaccuum, I pumped about 7 oz freon into it. Then waited 10 minutes, then started the car and turned the AC on(it was blowing warm). Then as I added the other 3 oz, I remember the Low vapor line got really cool and the air was blowing cold so I was thinking its good..*then it started to pour rain* so I turned the car off and stopped charging the system. Then, I came back to the next day and started the car expecting there to be a pressure difference like a normal undercharged system but it was behaving this way, so since then I havent bothered to add more refrigerant. All in all, the system has about 10 oz of refrigerant. Also, if there was a severe undercharge, I do not think the clutch would spin at all.

like cusser said, also make sure you are getting a good connection with your quick connectors on the service ports and that both the knobs on the quick connector are turned fully CLOCKWISE. and make sure both knobs on your manifold gauge set itself are closed when checking pressures. If you look under the hood and have the car running without the a/c on, and then keep looking at the a/c compressor (seeing the front of the pulley) while someone hits the a/c switch you should suddenly hear a type of click and the piece on the front of the pulley which was once stationary will now be turning.

Hi...new to ac recharging. I have done an awful lot of complex automotive repairs, including rebuilding an engine from bare block, and overhauling every part of an automatic transmission. I have replaced brake lines, replaced hub bearings, a timing belt, all suspension and steering components etc. Never any ac work, except buying a couple of little cans of 134a and letting them get sucked in.

Anyway...decided to do it right...bought manifold gauge set, vacuum pump, recovery tank, full 30 lb 134a tank, electronic leak detector (sniffer), uv dye light and glasses.

Set up gauges, turned on vacuum pump - got down to -29 psi almost immediately. Let vacuum suck for about 30 minutes (just to be sure any moisture in the system would boil off). Watched static vacuum...stayed at -29 for over 30 minutes. Started recharge. Charging low side only. Opened tank valve and the pressure on low side jumped to 70 psi instantly. Started vehicle...compressor clutch wouldn't engage at all. Jumped the relay terminals...got the clutch to engage continuously. Continued recharge. Ran recharge with the relay jumped for about 5 minutes. Removed jumper and put relay back in. Started vehicle...the compressor would now cycle on. It would come on about every 10 seconds for maybe 1.5 seconds. This never changed. Continued recharge with the pressure reading 70 psi still (never any change). Closed the tank valve and opened the high side gauge - both sides read 70 psi. With vehicle running and the compressor engaging and disengaging as described above, the pressures remained static and the same on both the high and low sides.

Continued this recharge and checked after 15 minutes, 30 mins and 45 mins...no changes to either the compressor clutching cycling pattern, the high and low pressure readings or the weight of the refrigerant tank. I concluded there must be something wrong with a component...(compressor??? orifice tube???)

Did quite a bit of research including looking at posts on this site. Found this one, and noticed someone had written to ensure the knobs on the service port connectors were turned all the way clockwise. I checked on mine and found they were ALL THE WAY COUNTERCLOCKWISE, such that the pins to depress the schrader valves were retracted, and the schrader valves were never opened.

I felt foolish, (but being new at this it's OK). I realized I had just fully vacuumed out and recharged the blue manifold gauge line only. It held vacuum really well!!!

I am done for the night right now, but will set it up again tomorrow (or so...we're having several days of cool weather...so no rush), and try to actually tap into the vehicle's system. I will update on any changes and results.

I am a little confused, however, as to why, when I had first hooked up the gauge set and opened both high and low gauges to their service ports, the static pressure read 20 psi (equally), then when I applied vacuum it dropped to -29 psi right away. I would think the hoses would be at 0 initially, (atmospheric), and not 20, which would mean there was still refrigerant in the vehicle's lines (even though I don't think I had ever actually tapped into them).

Oh well...I will see what the static pressures are tomorrow (or so) when I actually turn the knobs all the way clockwise, and try to get this done.

I was almost all set to order a compressor component kit and a condenser, but held off, opting to search out more information on the Net, when I came across that important tidbit in this thread...THANK YOU VERY MUCH FOR EXISTING!!!!

You also need a refrigerant scale to charge this accurately. Modern vehicles don't hold very much refrigerant and are very sensitive to the amount of charge. Just an ounce or two either way can and will cause problems. Charging with a manifold gauge set and a 30-pound cylinder is just a guessing game that could result in costly system damage. Gotta get yourself a good scale, too.