Automotive Air Conditioning Information Forum (Archives)

msmith_infl on Thu August 16, 2012 8:38 PM

Year: 1995
Make: Nissan
Model: D20 Pickup
Engine Size: 2.4L
Refrigerant Type: 134a
Ambient Temp: 87
Pressure Low: 120
Pressure High: ?

Hi all, Looking for a little help, hoping for good news, ready for not finding it...

Any ideas why the low pressure is that high when the outside temp is only about 87? I had figured the system had just developed a leak and I was going to be lazy and just top it off with a small can to see if it made a difference, but I decided to check the pressure first and wasn't expecting to see it be high like that.

I thought I had some old 134 gauges around, but couldn't find them. So, all I've got handy is one of the interDyamic gauges that attach to a can, so don't have the high side reading. The "low" side is an approximation due to just eyeballing the gap between 100 and 150 lbs on the cheap retail "gauge".

Is it possible that a low liquid level could cause the low side to be that pressure (about 120ish) ? This was taken at idle, engine at temp after 20 min. drive home from work, A/C turned on, high fan, low temp setting, compressor was turning, both tubes quite warm to the touch, but not really HOT. There was a little bit of cool air when I started home, but gradually became hot so I turned it off until I got home.

This little pickup has beeng going great for a long time now, but just the last couple of days (literally - 2 days) the A/C quit working.

It's been quite a while since I've needed to work on an A/C, and I've had lots of many reasons to forget whatever I was lucky enough to have picked up, so...

hay-ulp! ;-)

Thanks,
Mike

mk378 on Thu August 16, 2012 10:04 PM

120 low side with the compressor engaged suggests the compressor is bad, it turns but it won't pump. In that case there would be a similar reading on the high side, basically nothing is moving in the system. You need to use proper gauges to confirm the diagnosis.

Cussboy on Thu August 16, 2012 10:40 PM

Quote
Originally posted by: mk378
120 low side with the compressor engaged suggests the compressor is bad, it turns but it won't pump. In that case there would be a similar reading on the high side, basically nothing is moving in the system. You need to use proper gauges to confirm the diagnosis.

Real gauge set, both low and high pressures at about 1500 rpm. And when was the last time you replaced the truck's fan clutch?

msmith_infl on Fri August 17, 2012 7:30 AM

Quote
Originally posted by: mk378
120 low side with the compressor engaged suggests the compressor is bad, it turns but it won't pump. In that case there would be a similar reading on the high side, basically nothing is moving in the system. You need to use proper gauges to confirm the diagnosis.
Yep, that's what I was thinking... The only thing that was giving me hope was because I looked at the Mastercool vapor pressure table linked to on one of the other sections of the forum. It seemed to say that the pressure should be lower than that. But, now I remember that the truck was at operating temp. Is that something you have to take into account when reading the table for ambient temp? The "ambient" temp of inside the engine compartment where the system is, instead of the "ambient" temp of where my thermometer sits. When I went back to the table, it seems to show the whole story - 95 to 100 deg F = 114 to 124psi. Right in line with the rest of the bad news.

Quote
Originally posted by: Cussboy


Real gauge set, both low and high pressures at about 1500 rpm. And when was the last time you replaced the truck's fan clutch?

Yep again. I was hoping there would be some likelihood that a really low level of liquid cause the same symptom of high pressure on the low side. I'm familiar with the basic operation of the system, but not enough so that I know where all the components are located and what different circumstances could exist if there's a small, long-term leak that just reached its limits. Just wishful thinking.

Thank you, both. I'll see if I can locate some gauges, and take the next step.

Mike