Air Conditioning question

[Ieatcamaros]

Thanks for the reply, Phil. I know that it is called an accumulator. Everyone around here where I live calls it a drier. I have just accustomed to saying that. Just wanted to clear that part up. Everything works fine as of now. For some reason, it decided to blow a little warmer air than normal the other day. It wasn't hot like the door was stuck open. Is there anything else that would make that low-pressure cut out switch de-energize the compressor besides low refrigerant? All the visual inspections I did checked out ok. While we are on this type of subject, what would make a car only blow on defrost? I don't think it's the switch cause it has done this ever since I converted it to carbed. And it was working fine beforehand. This is on a 89 mustang.

**Could you tell me what the hell an orifice tube does for the a/c system?

[Philossifer]

Originally Posted by Ieatcamaros

Is there anything else that would make that low-pressure cut out switch de-energize the compressor besides low refrigerant? All the visual inspections I did checked out ok. While we are on this type of subject, what would make a car only blow on defrost? I don't think it's the switch cause it has done this ever since I converted it to carbed. And it was working fine beforehand. This is on a 89 mustang.

**Could you tell me what the hell an orifice tube does for the a/c system?

The blend door doesn't necessarily have to be stuck fully open, maybe it didn't fully close. Even a small opening from a blend door that's not tightly closed will allow enough hot air into the duct to warm up the air that has been refrigerated.

There are a several reasons why the clutch would not engage:
1) Low Pressure because of a low refrigerant level
2) The Low-Pressure Cut-Out Switch is out of calibration (with R-134a, it should shut off the compressor at 19psig and with R-12 it should cut off the compressor at 25psig.
3) Defective Low-Pressure Cut-Out Switch. It's screwed into the accumulator and has a (two wire) plug connected to it. (BTW, if you unplug the plug from the switch, there is a small screw recessed in there; this is the adjustment for setting the pressure cut-out point)
4) Compressor clutch gap is too wide
5) Compressor clutch coil is defective (weak or shorted)
6) Compressor relay is defective
7) Wide Open Throttle Switch is defective (at wide open throttle, this switch de-energizes the compressor clutch so the engine has more power)
8) On R-134a systems, there is also a High-Pressure Cut-Out switch that shuts off the compressor if the high side pressure exceeds about 375psig. If your radiator cooling fan is not working properly, this could cause the high side pressure to shoot up and cut off the compressor. Also, a dirty condenser or a missing air deflector could cause the same problem. R-12 cars don't have a High-Pressure Cut-Out Switch.

On a side note, I like to seal the parameter gap between the condenser and the radiator with foam so that the air being pulled by the fan has to get sucked through the condenser first. Without the seal, air can be pulled only through the radiator (through the gap) so that cool air doesn’t pass through the condenser. That’s one reason why some cars cool good while driving but not when their stopped at a red light. Also, (if your car has a belt driven fan) it’s important to insure that fan clutch is working properly so that there is sufficient air flow through the condenser. If you want you’re a/C to work, the fan clutch should be replaced if the car has more than 35 or 40 thousand miles on the odometer. As far as the A/C goes, the fan clutch doesn’t last much longer than that; even though the car is not overheating!

If your car has an electric radiator fan, there is a low and high speed, make sure it goes into high speed when the A/C is turned on.

As for your problem about only blowing on defrost…. I assume you mean, air only comes out of the defrost vent regardless of where the selector is set? Again, this is a vacuum problem. The diverter that controls where the air goes is vacuum operated. Maybe you’ve got a leak or maybe you don’t have sufficient vacuum. Might need to add a vacuum can.

You asked what an orifice tube does…. The orifice tube (or O-Tube) introduces the pressure drop between the high side of the system and the low side. It’s basically a controlled restriction in the system. At the high side of the O-Tube, the refrigerant is in a High Pressure liquid state. After passing through the O-Tube, the refrigerant is in a Low Pressure liquid state. This low pressure, liquid refrigerant then goes to the evaporator where is picks up heat (from inside the car) and boils back into a vapor. That’s how it cools.
Hope this wasn’t too much for you to digest but now you know why A/C work isn’t really a do-it-yourself job; unless you’ve got a lot of knowledge and experience in these systems.
Phil

[Maroon 5.0 LX]

The primary function of the receiver-drier is to separate gas and liquid. The secondary purpose is to remove moisture and filter out dirt.

Here is a good site that explains the different components of your AC system: http://www.familycar.com/Classroom/ac1.htm

[Philossifer]

Originally Posted by Maroon 5.0 LX

The primary function of the receiver-drier is to separate gas and liquid. The secondary purpose is to remove moisture and filter out dirt.

Here is a good site that explains the different components of your AC system: http://www.familycar.com/Classroom/ac1.htm

That's a good point but most Fords don't have a Receiver/Drier. They have an Accumulator.

A Receiver is located on the “high side” between the outlet of condenser and the inlet of the evaporator. Its main purpose is to store liquid refrigerant so the metering device always has a supply of liquid refrigerant. The expansion valve (orifice) in a receiver/drier type system will not work with vapor; it can only meter liquid. The Receivers secondary function is to remove moisture from the refrigerant. Usually, systems that have a Receiver aren't critically charged; in other words, the amount of refrigerant in the system is (to a certain degree) does not have to be within specs. The expansion valve can meter the refrigerant regardless of what’s happing on the high side, so if the high side is a little too high because of too much refrigerant, the system will still cool properly.

An Accumulator (on the other hand) is located on the “low side” between the outlet of the evaporator and inlet of the compressor. Its main purpose is to keep liquid refrigerant from going to the compressor. Liquid can not be compressed so any liquid refrigerant that finds its way back to the compressor can/will severely damage it. Accumulators also have a desiccant bag in them which absorbs moisture from the refrigerant. This type of A/C is a critical charge system. Too much refrigerant will flood the evaporator with liquid refrigerant and not enough will starve the evaporator.

Not trying to be a smart-ass but a lot of people mistakenly call an accumulator a receiver and vise/versa.
Phil

[Ieatcamaros]

Not trying to be a smart-ass but a lot of people mistakenly call an accumulator a receiver and vise/versa.

Good to know there is a difference. Thanks for pointing that out and for the quick rundown of an A/C system.

As for your problem about only blowing on defrost…. I assume you mean, air only comes out of the defrost vent regardless of where the selector is set? Again, this is a vacuum problem. The diverter that controls where the air goes is vacuum operated. Maybe you’ve got a leak or maybe you don’t have sufficient vacuum. Might need to add a vacuum can.

Yes, that is my problem. Where does this "diverter" get it's vacuum source, particularly on an 89 gt?

Thanks for the link, Maroon5.0.

[Philossifer]

Originally Posted by Ieatcamaros

Where does this "diverter" get it's vacuum source, particularly on an 89 gt?

Thanks for the link, Maroon5.0.

To be honest, I'm not real knowledgeable about the vacuum routing on these cars. I do know for sure that the temperature blend door is controlled by a cable, but the switch that selects where the air goes (vent, floor, defrost, etc.) is vacuum controlled.

I guess the first place to start is by determining if you have enough vacuum. (Do you have a brake bleeder like a "MightyVac”?) They're pretty cheap and well worth the investment, plus they’re great for testing for vacuum leaks.

On the firewall is a “Vacuum-Tree" that gets its source of vacuum from the intake manifold. From there, the Tree sends the vacuum to deferent places where it's needed on the car. One place is the A/C Heater control in the dashboard. Hook-up the MightyVac to the Vacuum-Tree in place of the hose that goes to the intake manifold. Pump up the vacuum and watch the needle on the gauge. It should hold the vacuum for several minutes. If the vacuum drops rapidly, you'll have to start checking all the vacuum hoses including the one leading to the heater control and the control itself. If it does hold vacuum, try operating the heater control with the engine off using the MightyVac as the source of vacuum. If the control works, then you know you don’t have enough total vacuum at the tree when the engine is running.

Maybe someone else can give you more information about checking out vacuum problem....Like I said; it's not really my expertise!
Good luck,
Phil

[Ieatcamaros]

After reading your reply saying that the diverter was vacuum operated, I started checking things out. Yesterday I noticed this little thing on the firewall (in the pic) had a line going into the dash down where the evaporator core is. I had put a plug on it (where the vacuum line is now). I took the plug off and put a vacuum hose on it. I can now select where I want the air to blow. My hat's off to you Philosofer. There is no telling where that thing originally got it's vacuum source, but it now comes directly off the vacuum tree/manifold. I put a pic up so if anyone else has this problem they can see what has to have vacuum before the diverter door will change directions.