Who knows stuff about A/C (air conditioning) systems?

[Zeus33rd]

Whats a sign/symptom of an A/C system needing a recharge? Does it just gradually not blow as cold? Or is it an abrupt change? Does the amount of charge in a system have any mechanical effect on the way the compressor engages/disengages?

I don't think it matters, but this is concerning my '04 Nissan Frontier. It's got 85K miles, and although I've only had it long enough to put 12k miles on it, it seems like it doesn't blow as cold as it used to, and the compressor seems to effect engine rpm's and power more than I remember, especially at idle. It could just be because it's soo damn ridiculously hot in Kansas right now that it can't keep up...kinda doubt it though.

And next question, is there a way I can at least check the system myself? I'd rather not take it somewhere just to pay to have the guy tell me it needs servicing.

 

[4X4HIGH]

Joe, i know enough to hurt myself but i'll offer up what i do know. There is a low pressure switch that when the charge is too low won't allow the compressor to engage (safety feature). Also when the charge is slowly lost the effectivness of the AC system starts to dimenish. Also when it's really hot outside even the best AC system will feel like it isn't working as good as it should. Check to make sure the AC compressor is still engaging when you turn it on, if not the first thing to do is jump the terminals temperarily to see if it wil now cylce on, obviously this is bypassing the low pressure switch and not suggested to leave it like that but testing purposes only.

 

[Zeus33rd]

Right on, thanks for the quick reply Scott.

I know the compressor still engages cause I can hear it and feel it- rpms drop. Does this on it's own and when I push the button on the dash. That means the safety switch is working to I suppose. Can I check the amount of charge myself? Or is that a shop only thing?

 

[Zeus33rd]

I just found this place with Google.

http://www.autoacsystems.com/_faqs/detail/quick.html

Pretty cool info there.

 

[K5 rockcrawler]

Make sure your radiator and condensor are clean and not full of bugs, dirt, grass, or anything else. The lack of air flow will hurt the performance of the air conditioning system.

 

[Blue85]

If the charge is low the compressor will cycle off more quickly. A quick qualitative check (without gauges) is to run the system for a few minutes and touch things. From wherever your orifice tube / expansion valve is, all the way to the compressor input should be cold (unless it's insulated, it should frost up on a humid day). If you can't find the valve, don't worry, that will be cold even with very low refrigerant, just check near the compressor. BE CAREFUL because the high side lines are very hot. Keep in mind I've never looked at this vehicle before.

Remember that the temp of the cold coil is directly related to the temp of the hot coil, so the hotter it gets outside and the worse your radiator fans work, the warmer the vent temps. If squirting the condensor with a hose helps the vent temps a lot, they system could probably use more airflow.

Also, are you using outside air or recirculated air (MAX)? It makes a big difference after you have been driving for a while. There is a limited temperature drop possible through the evaporator, so if you can start with air that is already cooler than outside, it helps a lot.

Don't try to add refrigerant without gauges.

 

[Zeus33rd]

If the charge is low the compressor will cycle off more quickly. A quick qualitative check (without gauges) is to run the system for a few minutes and touch things. From wherever your orifice tube / expansion valve is, all the way to the compressor input should be cold (unless it's insulated, it should frost up on a humid day). If you can't find the valve, don't worry, that will be cold even with very low refrigerant, just check near the compressor. BE CAREFUL because the high side lines are very hot. Keep in mind I've never looked at this vehicle before.

Remember that the temp of the cold coil is directly related to the temp of the hot coil, so the hotter it gets outside and the worse your radiator fans work, the warmer the vent temps. If squirting the condensor with a hose helps the vent temps a lot, they system could probably use more airflow.

Also, are you using outside air or recirculated air (MAX)? It makes a big difference after you have been driving for a while. There is a limited temperature drop possible through the evaporator, so if you can start with air that is already cooler than outside, it helps a lot.

Don't try to add refrigerant without gauges.

Wow, great reply. Thanks!

Hmmm...I don't know if it's on recirc or outside...lol. My guess without going out there to look, is it's just outside air. Now I finally know what that recirulation/MAX thing is all about...I never knew till now.

Also, does the puddle of water the accumulates on the ground after running for awhile say anything about the "health" of the system?

Is there anything I can do to improve "vent temps" when the vehicle isn't moving? Maybe an electric fan on the condensor? <- that's the radiator lookin thing right?

 

[4X4HIGH]

Electric fan in front of the condensor will help at idle. That vehicle is new enough though that it probably has an electric fan anyhow. All AC systems that i've seen where an electric fan is used on the engine will turn the electric fan on when the AC compressor is commanded. That is something that you could check for though, make sure any electric fan behind the condensor turns on when the AC is on.

 

[Mike D]

A lot of good info has been written here. Also Many vehicles use an electric fan in front or behind the condenser (and radiator) when the compressor engages. It turns on when the system pressure rises above about 175psi and cycles off at 125psi. If your Nissan has a fan, is is working? If it is burned out your AC performance will be lousy.
Also as a side note the automotive engineers disign AC systems to drop the cabin temperature 20 degrees F lower than the outside ambient temperature. So on a 90 degree day the cabin temperature will be about 70F. The key thing about AC is that it essentially removes all the humidity from the air so you feel dry and comfortable.
Another thing you might want to check is to make sure the heater core doors are closed. Any heat that is leaking past the flapper doors and mixes with the AC air will reduce the cooling effect.

 

[Zeus33rd]

I went out and checked it out a bit ago...The lines were cold to the touch. That's a good thing I'm assuming. I had it on outside air...never even noticed the recirculation button till today... I'll have to give that a shot tomorrow. And there's no electric fan on the condensor. Only the normal engine driven one.

 

[gone huntin]

Check the high side line from the condensor to the compressor on the driver's side for oil on it. They are bad about leaking from the crimped ends. That's the only place I ever see leaks on the Frontiers/Xterras. By the way, I'm a Nissan master tech if you have any more questions.

 

[Zeus33rd]

Check the high side line from the condensor to the compressor on the driver's side for oil on it. They are bad about leaking from the crimped ends. That's the only place I ever see leaks on the Frontiers/Xterras. By the way, I'm a Nissan master tech if you have any more questions.

Oooo....So what should I expect to be paying for a a/c service at the dealership? The guy today told me $80-90...is that about right?

 

[gone huntin]

Is that for a performance test or actual servicing including freon? Our labor rate is $92.50/hr and r134a is $18/lb. We charge 1/hr for an evac/recharge.

 

[rjfguitar]

Joe,

A/C's are an expensive luxury at times. $100 sounds about right to vaccuum and recharge the system. You can dump a grand into a system at the dealership fairly easy.

You mention you are noticing RPM change at idle more than you used to? Might be that the system is low on freon and it is cycling faster. The lower the freon level, the faster the compressor will cycle, until the pressure switch eventually keeps the pump from running at all once there is too little freon left in the system.

Check the tag under the hood that should be on the radiator support, it should tell you the quantity of freon that the system holds. If it's large, like around 3 pounds, then you might try getting a cheap "recharge" kit that they sell at the autopart stores. Add 8-12oz and see if that helps it out and slows down the cycling of the pump, and obviously brings down the air temp. If the pump continually runs without cycling at all, then you likely have too much in it. At that point, take it to an A/C shop and have them check for leaks and recharge it. If it is like our Dodges and only holds 1lb/8oz, basically forget it. Having just a couple oz too much or too little and they work like garbage. You need to completely vacuum them out and use an A/C machine or digital scale to get the exact quantity into the small systems.

 

[BGKYK5]

You can dump a grand into a system at the dealership fairly easy.

In fact we did just that on my wife's car when the compressor took a dump last week.

I never buy aftermarket warranties, but I did for our '01 Caravan that we bought used in '04. It has paid for itself several times over so far. It paid $1100 of our $1300 bill this time (which included an evap line replacement and power lock actuator replacement as well).

 

[lectric80]

Also, does the puddle of water the accumulates on the ground after running for awhile say anything about the "health" of the system?

It really doesn't say much about the health of the system, except that refrigerant is cycling. Under normal operation the a/c system pulls the moisture out of the air before it enters the cabin, providing cool dry air. When you stop and shut the engine down, that moisture on the evaporator is just draining out.

Everything people have told you in this thread is true and correct. Amazing how much good advice people have on this board.

 

[Zeus33rd]

Is that for a performance test or actual servicing including freon? Our labor rate is $92.50/hr and r134a is $18/lb. We charge 1/hr for an evac/recharge.

Dooder said "it's about $80 for the service, +freon on top of that." He also said it would take a couple hours. Never said anything about a "performance test". I didn't know there was such a thing.

 

[Blue85]

Also, does the puddle of water the accumulates on the ground after running for awhile say anything about the "health" of the system?

Is there anything I can do to improve "vent temps" when the vehicle isn't moving? Maybe an electric fan on the condensor? <- that's the radiator lookin thing right?

The puddle of water says that it is working. Cold air holds less moisture than hot air (come to think of it - moisture condenses on the evaporator and evaporates on the condensor).

Anyway, anything you can do to improve airflow through the condensor will drop the vent temps. Make sure the fan clutch is good and the shroud is intact. You might be able to perform some sealing around the edges of the condensor and radiator to make sure no air bypasses the condensor. Also make sure the fins on the condensor are clean and straight.

You also gain by reducing the sun load, i.e. window tint, etc. But if you haven't been using "Recirc" or "Max" I think you will be pleased with the difference on longer trips.

One more tip - to find leaks, just look for oil. The oil to lube the compressor is carried all through the system by the refrigerant, so when refrigerant leaks out it leaves some oil there. But honestly it sounds like your system is fine or only has a very minor leak. Very minor leaks aren't really worth fixing. Just top it off once a year.

 

[Zeus33rd]

I spend a lot of time just sitting in my truck, parked. So I'm most interested in making vent temps colder in that situation. It sounds like a fan of some sort on the condensor, wired to a switch in the cab would be a good idea.

I just made the appointment to get it serviced...I hope I'm not wasting my $100.