AC Chirps, no longer cold???.......

[hooterville]

Yesterday, I was sitting at idle and the AC went from cold to hot. I figured that it needs a recharge with r134a. I go to charge the system and it doesn't accept the refridgerant. I'm guessing there is too much pressure. I am using the line that is directly above the compressor (the low pressure line, right?). After that, I shut the car off and started it again and I heard a chirping noise in the engine bay, it was coming from the radiator. What is that noise? Also, what do I do to get my AC recharged? Please help, it was 102 today!

 

[hooterville]

The fitting that I used was against the firewall underneath the plastic housing.

 

[projectSHO89]

Uh, thats the high pressure line. You want to turn that 12 oz can of R134 into a hand grenade or what? That's what you can have when 200+psi hits it.

The charge hose fitting should be made to ONLY go on the low side fitting. At the firewall.

Steve
89

 

[sdpatt]

Are you sure the chirping noise isn't coming from the serpentine belt slipping over the compressor pulley. If you have a 3.0L then just tighten the belt, but if you have a 3.2L, the compressor may be on its way out.

 

[hooterville]

I don't think it's coming from the serpentine belt because I hear it coming from the front of the engine bay. It chirps seldomly on start up, I thought it might be the ac clutch grinding. I still don't know why it won't accept the AC recharge?

 

[rangerj]

Hooterville,
The chirping noise may be the bearing in the compressor pulley. In the early SHOs there is a replacement bearing available as a separate part. I know this applies to 1989 and 1990. As for 1991 and forward, you may have to replace the whole A/C clutch package, that is the coil, pulley, and front disk. The clutch pulley bearing on the Nipondennso compressor is an odd size. The bearing is made by KOYO, and if you can match it you can expect to pay about $30.00 for it. As mentioned earlier, it is available for the early years. 89 and 90 I am sure of. The other years I do not know about.
Next, you may not be able to put a charge in your A/C system because the low pressure condition is not allowing the compressor to engage. You can "jump" the low pressure wires and cause the compressor to engage. This should allow you to put a charge into the system. However, if you have a need for a charge, you must have a leak in the system. The leak may be so slight that you can put in a charge and it will last a long time. Keep in mind that leaks do not get better with time, they get worse. Also keep in mind that the oil circulates through the system with the refrigerant, and if you are leaking refrigerant then you are also leaking oil. It is the oil that attracts dirt to the place of the leak, and it is that fine black oily residue that tells us where the leak is (usually).
Do a pressure test on the low pressure side, without the engine running, in order to determine if there is any pressure in the system. If the system is dead empty, then fix the leak, and vacuum the system down to 27 to 30 inches of vacuum, for at least a half an hour. We vacuum the system in order to remove air and the contaminents in the air, especially moisture. You do not want moisture in your A/C system any more than you would want water in your crankcase. Then put in a fresh R-134a charge. You can add oil when you have the system open, for fixing the leak, or if you are simply going to add a charge, then add a R-134a charge that also has a few ounces of oil. Hooterville sounds like my kind of town! Hope this helps. rangerj (Jack)

 

[sdpatt]

You haven't mentioned what the system pressure was. With R134a, a good ballpark is 250 psig on the high side and 50 psig on the low side at idle and an ambient air temperature around 85-90F degrees. The hotter the air and the engine compartment, the higher the pressure will be due to expansion of the gas. Youmust have a pressure gauge to properly charge the system.

Scott

 

[hooterville]

Now, if the system was leaking, wouldn't I have felt a change in temperature slowly to where it only cool and then warm. The AC went from ice cold to HOT. I was sitting in a parking lot with the AC on and the temp was about 103 degrees. I heard that it might be a bad temperature sensor in the system. By the way, it is a 1994 SHO ATX.

 

[hooterville]

All right, I tested the system pressure today. The low pressure line is the line directly above the dryer, correct? I tested that line and the pressure was an astounding 140 PSI. I also noticed that as soon as the AC kicks on, I can feel cool air, but when the fan kicks full blast it is very hot. I want to know your opinions on this, especially sdpatt's.

 

[hooterville]

Checked it again and the pressure actually rises when the AC is turned on. Should I attempt to evacuate the system to normal pressure immediately or what?
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Here's some pictures of my car, 94 SHO ATX.
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[rangerj]

Hooterville,
If you are getting high pressure readings from the low pressure (suction) side of the A/C system here are a few suggestions on what to check for; 1) inadequate airflow across the condenser - is the condenser clear of dirt, bugs, leaves, etc.? Is the fan(s) running at a high enough RPM to pull enough cooling air across the condenser? Maybe the chirping noise you thought was coming from the radiator was a fan(s) motor bearing, or some other problem with the fan or its motor.
2) Is the engine overheating, or running at higher temperatures than normal? Does the temperature rise when you are standing still, say at a stop light, then come back down when you are moving? This also would point to the fan(s) or something in this system, e.g. temperature sensor.
3)If the pressure readings are normal on the high side, but high on the low side, it could also point to the orifice tube being bypassed, that is the refrigerant is leaking around the "O" rings.
4) The A/C suction line partially restricted or plugged. If the pressure reading is taken at the accumulator and the restriction is downstream of the service access valve.
5)Poor performance of the compressor itself. Maybe the chirping is the belt slipping on the compressor pulley because the compressor is dragging. With the belt off of the compressor, it should take 7 foot pounds, or less, to turn the compressor. The best way to measure this, in my opinion, is with an inch pound torque wrench. 7x12=84 inch pounds of torque. Even if the compressor turns easy enough that does not mean that the cylinders and/or other internal components are not worn out!
Lastly, Scott is absolutely correct. The system should be tested with a set of guages. It takes a minimum of 20 PSI to activate the low pressure switch, but you should be looking for 20 to 60 PSI on the low pressure side depending on the ambient temperature. Ambient temperature is the temperature surrounding the system, that is the under hood or engine compartment temperature. Scott's recomended 50 PSI is a good goal to shoot for.
On the high pressure side look for pressures in the range of 175 to 300 PSI, again depending on ambient temperature. Use Scott's high pressure goal here as well. You can't argue with success, Scott is getting air coming out of his vent at near freezing. It does not get any better than that.
If you can get a vent temperature that is 40 degrees colder than the outside air temperature then your system is working OK. It may not be perfect, or the best that it can be, but it is acceptable. Hope this helps, Jack