96 Q45 AC not cooling

[GuidoInc]

1996 Q45 100K milesThe air from the AC is sometimes slightly cooler. I added freon with no change. I checked the low speed of the condensor fan and it turned on when I applied battery power to it. I am having trouble with the vehicle speed sensor. It was replaced but the speedometer has been working about half the time.

If there is trouble with the vehicle speed sensor will this effect the AC cooling?

Any ideas on what else I can check?

Thanks all

[maxnix]

If you added freon only (which you shouldn't as Freon is a trademarked name for R12, and all 1995 and 1996 Q45 use R134a), you merely treated the symptoms, not the cause.

Search the previous posts and you will understand how your problem should be addressed depending on the previous maintenance you have performed.

[autotech43]

You need to have the high and low side pressures checked, technicians can pinpoint the exact cause by doing so. That particular compressor has a swash plate that moves back and forth controlling the refrigerant to the evaporator, if it sticks in the low or high volume level, the expansion valve inside the evaporator cannot accomodate the low or high level of refrigerant. Another cause, the system could be contaminated by some things causing the expansion valve to not function properly. I have seen A/C driers fail, along with internal compressor failures to a point where the expansion valve, A/C drier and the compressor ALL need replaced. Another note, 134A type refrigerant is real finicky on having the correct charge of refrigerant, where the R12 type refrigerant is more forgiving. Just some info(years ago, some of the older Nissan vehicles had what they call a suction throttle valve that worked in conjunction with the expansion valve to help prevent evaporator freeze up). Have the system checked by a qualified tech, diagnose it correctly, replace the parts, you'll be glad you did. Its your money!!!!!!

[GuidoInc]

Another symptom that is happening is if I press the "off" button pause a few seconds then press the "auto" button some cool air will start to flow.

Thanks all for your info.

[natsoundup]

What is the role of the expansion valve?

[DAEDALUS]

The expansion valve meters refrigerant into the evaporator, where the liquid turns to gas, absorbing heat in the process. I rarely see it reported on this board, but occassionally they can get blocked.

[GuidoInc]

If I turn on the AC shouldn't the condensor fan come on? It doesn't come on but when I connected it directly to the battery it came on.

[natsoundup]

thanks...daedalus....I think I have a partially block valve.... refirgerant is at correct levels....

....just seems to take the car a little longer to get cool....replaced the drier and compressor a couple of months ago..... I got through the tough part of the summer pretty easily....now it's a non issue..... but next spring, I may do the expansion valve.....

Once you drive it a few miles at 2k rpm or so...it blows much cooler... today it was in the low 80's and it still took a minute and a half or so to blow ice cold. 90's it may take 3 or 4 minutes...but it does get very cold.....

...if my transmission holds up..... realistically I don't think I will have the car next air conditioning season....... but I wanted to know what that part did...

[autotech43]

The condenser fan won't come on when powering up the A/C compressor until a certain temp is met. Years ago (nissan ) tied the condenser fan to A/C via relay to operate at the same time.

[DAEDALUS]

I'm not certain about the '96 Qs, but on the '90-'93 models there are 2 switches in parallel to the condenser fan relay--a temp switch that autotech mentioned and a pressure switch. If either of these is tripped, the fan should come on. It is the pressure switch that causes the fan to come on when you turn the AC on since the pressure jumps up right away. If the pressure in the system is normal with the AC on but the fan is off, then either the fan is bad, there is a wiring harness open circuit, you have a bad relay, or you have a bad switch.

[Q45tech]

R134a charge is extremely sensitive to weight! Being off 5% can make a significant difference, same with the system oil ........a single ounce [out of 7] can adversely affect things.Usual problems of not vacuuming the system down LONG ENOUGH to boil all the moisture out.......30 minutes minimum. Leaving the receiver dryer open to the air for over 3-5 minutes during install.

The system needs 5 minutes [at 60 mph] to bring a 110F vent temp down to 60F and another 5 minutes to get below 50F.