A/C goes warm when going up a hill and other high engine loads. If anyone else has had this issue and has corrected it please let me know how you fixed it. I have the 2.5L automatic if that helps.
I have read that this can be normal for a lot of cars but the threshold of this happening seems to happen far too easilly. If you know of a way to adjust it please let me know that too. Thank you.
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[This message has been edited by RACE (edited 08-26-2013).]
Nope, Fiero's don't have vacuum AC controls. Are you at full throttle when this happens? IIRC the computer turns off the compressor at full throttle. Also, what year car?
It's an 87. It happens long before full throttle. On a straight road today the air con was really cold at 62 mph but at 70 mpg it got warm inside. I suspect that there is some type of vacuum cutout somewhere.
The computer gets a signal from the MAP sensor all the time, but I don't know what is in the software. It would be very easy to stop the compressor if the vacuum goes down...or is it up?...in the engine. This could be an indication that your engine is not making the power it used to make. Maybe a simple tune up would fix this.
The engine is in good tune. My exhaust is old and I suspect that the cat may not be as open as it used to be but even so, it shouldn't cut out my a/c that early.
The ground for the AC clutch relay terminates at the ECM. This gives the ECM the ability to drop the ground and turn off the A/C. Normally its stated this is to turn it off at WOT, to help protect the compressor, but who really knows how it is handled with the 4cyl. Since the 4cly isn't blessed with excess power, it may disable the A/C sooner to allow it to put more power to the wheels under other high load conditions that might not be WOT.
my A/C goes warm after about 30 minutes of highway driving.
thanks
I am not overly impressed with the LS4 compressor with a variable orifice. Its cool and will keep you from sweating, but I wouldn't call it good. I though something was wrong till I looked it up in the service manual. The maximum vent temps for ambient temps/humidity are listed in a chart. On a 86-95 degree day, here are the max temps based on humidity: Below 30%: 59 degrees 30-50%: 63 degrees Above 50%: 66 degrees
The best thing to do then is to get rid of the 4 cylinder then. ; ) That will happen eventually but its starting to sound like I will have have to live with it the way it is for now. I get better mileage at 62mph anyway.
If its based off of manifold pressure and not WOT then a vacuum leak could potentially create a premature wide open intake absolute pressure. My cruise control has never worked. Maybe its time to look into a possible leak in that system.
Originally posted by fieroguru: I am not overly impressed with the LS4 compressor with a variable orifice. Its cool and will keep you from sweating, but I wouldn't call it good. I though something was wrong till I looked it up in the service manual. The maximum vent temps for ambient temps/humidity are listed in a chart. On a 86-95 degree day, here are the max temps based on humidity: Below 30%: 59 degrees 30-50%: 63 degrees Above 50%: 66 degrees
The 87 2.5 does kill the a/c comp at about 4600 RPM but unknown on throttle position. If it is like other setups, usually 75% throttle or above will disengage the compressor. Funny thing is, fuel cut is at about 5600 RPM.
Another thing to consider is a slipping compressor clutch. Slipping at normal operating speeds may not be noticeable, but while accelerating and higher RPM runs, the clutch can slip if worn or the air gap is not set correctly. I would have to say the clutch is worn.
Fieroguru, if this is the stock LS4 a/c compressor, I believe that it is of the variable displacement design. These work best with a fixed orifice tube.
[This message has been edited by chetw77cruiser (edited 08-26-2013).]
I have a brand new compressor so really dont think that its slipping. Thee vent temp is 42 degrees when it's not cutting out. It's air colder than I thought it would have been. I'm not even sure if that's a good thing for the system.
Originally posted by chetw77cruiser: Fieroguru, if this is the stock LS4 a/c compressor, I believe that it is of the variable displacement design. These work best with a fixed orifice tube.
Thanks
That's the answer Ryan gave me about the LS4 compressor.
I used to have a 96 Camaro with the 3800, the compressor shutoff was way before WOT. Felt like maybe 50-60%. I guess this was to preserve the throttle response because of the car's sporty intentions.
Something you can do to keep the cabin cooler is to run the system on MAX. This closes the door for outside air intake and recirculates the inside air. Rather than trying to heat 85 degree outside air, you start to re-cool air that may be in the 70's. Works like your home AC. Keep the windows and doors closed and your house stays cooler. Running the AC on NORM brings in the outside air, including some of the heated air from the radiator, which can pass around each side of the front compartment seal, along the fenders. Some people think that the MAX position keeps the compressor on all the time, but that's not the case. It cycles the same as when set at NORM.
Originally posted by fierofool: Some people think that the MAX position keeps the compressor on all the time, but that's not the case. It cycles the same as when set at NORM.
MAX will actually run the compressor less once steady state is reached. Once the air becomes sufficiently cooled, the pressure on the low side of the system will drop enough to trip the low pressure switch, and the compressor will begin to cycle.
If its based off of manifold pressure and not WOT then a vacuum leak could potentially create a premature wide open intake absolute pressure.
No. The only thing that could cause that would be a disconnect between the intake manifold and the MAP sensor. A manifold vacuum leak has virtually no effect while driving, except at or near fully closed throttle. Think about it. While driving you will automatically (and unconsciously) compensate for any vacuum leak by reducing the throttle slightly. (It may help to think of the throttle itself is a big, driver-controlled vacuum leak.)
[This message has been edited by Marvin McInnis (edited 08-27-2013).]
There are three things that will cause the compressor to shut off: 1) ECM at high throttle. I always thought it was for performance/safety too, but it does it at basically wide open throttle more or less. 2) Low refrigerant pressure. If you do not have enough, the compressor will draw down the pressure and the switch will open. This is the switch on the canister in the front trunk. 3) High refrigerant pressure. Not sure how this one would happen, but it is a safety feature.
Of course, the opinions of a slipping clutch are on the money. If the clutch is powered and you get warm air, then the clutch is not holding.
All the ways to find out which one it is are a little dicey since it happens while driving. You need to connect to the wires of each switch and see which one opens up. A small light bulb across the switch will illuminate if the switch opens. It is easiest to test the switch in the front trunk since you can bring test wires through all the seals in front. Don't have a wiring diagram here at work, but the ECM is likely to be either at the top of the chain or the bottom. That makes it pretty easy to see if it is the one doing the cut out.
You can probably tell pretty quickly if it is the low pressure switch by just putting a gauge on the low pressure side of the cannister. Have someone rev up the engine while you watch the pressure. You will for sure hear it if the switch opens. You can borrow a gauge from AutoZone. You pay for the gauge and then get a refund when you return it intact.
An overheating coolant will cause that, some times the headgasket start to fail only on high rpm, or heavy loads, increasing the temp of the refrigerant at the radiator and causing the high preasure switch to shut off.. Even if you don't notice any coolant leaks, it may be compression or exhaust going to the coolant passage.
My red herring..... Check the TPS for smooth ohms and then voltage. The ecm may think your mashing the go fast juicer all the way.....when your not. It probably isn't the right answer, but I thought i'd throw something in here anyway!
As far as hot coolant goes I don't think that will ever be an issue. I have already installed a 3 core aluminum radiator in preparation for an eventual engine swap. The needle never moves. I'll check on some of the things that you have recommended and let you know if anything changes. Thanks guys.
I'll check on some of the things that you have recommended and let you know if anything changes. Thanks guys.
