Anybody know the specifics of the 95's air conditioning system? My car has lost it's ability to cool over the last couple of years. Got a guage set and at 2000rpm I had a low pressure of 50 and high side of 145 at 92 degree ambiant temp. Vent temps around 65 degrees.

After getting some suggestions on A/C board I decided to add refridgerant to try and get high side in appropriate range. After adding 1 can of R134a I got high in the side to 170 and low went up to 65. Vent temps remained around the same. A/C board says it's the compressor and their probably right, but I was wondering if anybody here had any other things to check before I do this.

Also does the service manual have pretty good instructions on replacing compressor? The Haynes and Chiltons have nothing.

 

Are you sure you have enough juice in the system? Add another can and see what happens. Sounds like your still low. I always remeber my dad putting 2 cans of juice (R12 back then) in moms buick each summer. Granted it's different (134a) now, but seems like you still don't have enough freon in there.

 

My understanding (i.e. very limited) is that the low side pressure determines how cold the system will be and rasing the low side pressure will increase the temps. Therefore I believe that adding more will decrease my cooling. The big problem is that you can't tell how much is in the system without evacuating the system and refilling.

 

My understanding (i.e. very limited) is that the low side pressure determines how cold the system will be and rasing the low side pressure will increase the temps. Therefore I believe that adding more will decrease my cooling. The big problem is that you can't tell how much is in the system without evacuating the system and refilling.

 

After looking in the '99 FSM, your discharge tempertature is not to far off (depending on relative humidity). The table indicates that at a rel. humidity of 60-70% and an ambient temp of 95 deg., the temperature should be 59-64 degrees.

Be aware that the discharge temp varies A LOT depending on ambient conditions and doing the proper testing procedure (running the engine at 1500 rpm's for 10 minutes with the a/c and fan on high). For instance, a 10% drop in humidity would be a 5 degree drop in discharge temperature.

The factory spec on pressures for 50-70% humidity and 95 degree ambient is 199-262 psi on discharge and 23-27 suction.

According to the FSM, with the high pressure side too low and low pressure side too high; you've got a bad compressor.

Here is the correct procedure for testing:
1. Test indoors or in the shade.
2. Doors: closed
3. Door window: open
4. Hood: open
5. Temp setting: Max cold
6. Discharge air: face vent
7. Recirculation switch: on
8. Fan speed: 4 speed
9. a/c switch: on
10. Engine speed: 1500 rpm
11. operate the a/c system for 10 minutes before taking measurements.

 

Don't rule out the Expansion Valve either!!! Thats cheaper then the Compressor. Verify that first.

 

A clogged expansion valve would give high pressure readings on both the suction and discharge sides. Also, the FSM says "An area of the low pressure pipe is is colder than areas near the evaporator outlet" and "plates are sometimes covered with frost".

 

Tested in shade, doors closed, windows open, hood up, fan on high, idled 10 minutes then ran at 2000 for 2 minutes. Relative humidity in the 80% range. No frost on any of the pipes low side pipe was cool but not very cold.

How can the expansion valve be tested? This is the kind of problem I am having... repair shop wants to replace compressor and see if that fixes it. I'm not sure if they know much about Nissans and don't want to spend money to replace compressor and still have problems.

What type of expansion valve does Nissan use?

 

I don't know if you can test it, besides the pressure gauge readings. The FSM doesn't have anything on testing just the expansion valve. You may want to find a different shop that has more confidence in their own diagnostic abilities.

 

Everyone... just looking, but I'm having AC problems, and the information gained from this thread is very very good. I'm gonna check my system again now when I get a chance since last time I checked, low pressure side was high... but I thought that just meant that I had enough refridgerant! Now I know what else to check before going for the $500 compressor change!

Thanks again sinewave, bobk, and all on this thread!

-V

 

Here is an ambient temp./high-low pressure table that you may find useful.

 

Your system is working correctly...
What you need to do is buy engine degreaser and go to that car wash place that has pressure hose...
spray the condensor real well then pressure wash it off..
That will help big time..
Did this on my Bimmer and got vent temp down 6-7 degrees.. Thing gets gummed up w/ crap and cools poorly..

 

Just be careful with the pressure washer, you can bend the fins and reduce the heat exchange even more than the dirt and bug bodies.

 

I cleaned it at the car wash prior to other testing, it was pretty clean at the time and didn't make much difference to the cooling. I remember reading somewhere that the maxima had some electronic contols that were not common (I think I saw it on a post in aircondition.com) but I wasn't able to find the information recently when I searched.

Thanks for everybody's help.