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Probably just because its going bad. I've heard different symtoms with our A/C compressors. Mine makes a whinning sound when the AC is on, and my dealer told me don't replace it until it completely goes out.

But to answer your question of "WHAT ARE THE REASON..."
It may just be going bad.
 

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so, you upgraded to the the 134? If so, what all do they change out when they upgrade it. Is the compressor included, and what difference did you notice?
 

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Cycling is usually due to low refrigerant charge....it may cycle when it is overcharged also.

The triple pressure switch (TP switch) acts on both too much and too little refrigerant.
When you have too little, the TP switch will stop the current going to the clutch in order, to save the compressor.
When you have too much it does the same thing.

When the system is at equilibrium, the pressures on both sides are equal. Usually there is enough pressure in the system so the the TP switch will turn on the compressor.
The suction and discharge lines, referred to as the HI and LO sides are just that, HI and LO pressure lines.
When you run the A/C, the suction (LO) line has gaseous (cold) refrigerant, so the pressure is Low. The discharge (HI) side has liquid (hot) refrigerant, so the presure is Hi. If you don't know what I am talking about look up Boyles law pv=t

When the A/C is running you should get pressures around 25psi for LO and 225psi for HI.

Now when your A/C is chugging along, the pressure on one side may drop or rise, so that the TP switch says "hey that's too low or that's too high, I'm killing the compressor".
So the system runs a little bit and the pressure drops down to within the specs and now the TP switch allows the compressor to turn on again. Repeat that, and you have cycling.

The gist of all of that, is, you may be close to one of the cut off points when your A/C is running and when it actually operates, it creates the situation of the compressor cycling.

You may also have air in the system.
When you let out the R-134a, you needed to pull a vacuum and boil out all the water in the system, then charge into the vacuum.
R-134 systems need 26.5oz of refrigerant.

How much did you put in ?

If more than 26oz, you may blow your relief valve or worse your compressor. :eek:
 

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CakeDaddy said:
so, you upgraded to the the 134? If so, what all do they change out when they upgrade it. Is the compressor included, and what difference did you notice?
When an R-12 is upgraded to R-134a, not much is really changed.
All the O-rings you can get to.
The lines, condense and evaporator should be flushed with brake cleaner and then blown out with compressed air to remove all oild mineral oil.
The compressor flushed with what oil you'll be using in you system (POE or PAG).
The dryer MUST be replaced and somtimes the expansion valve (gotta rip apart your dash to get to it - I didn't do mine).

System take 8oz of oil and 26.5 oz of R-134a.
Once all parts are cleaned and system put back together, pull a vacuum for atleast 1/2 to make sure vacuum holds (more is always better).
Recharge system into vacuum (car off) until system does not "pull" refrigerant anymore, then start car and fill to ~24oz (usually 2 cans).

To actually answer your question, if the part does not need to be changed, then the person performing the retro, will not replace it unless it is failing or you want to pay for new parts. Usually, just O rings, fittings and new oil put in (with old oil still there - this is bad :(), fittings glued with lock tite.

BTW the same compressor is used on both R-12 and R-134 systems (although they have different PN's). All that was added was a "relief valve" which is part of the manifold. If pressures get over 360psi (I think), the valve will blow and you need a new one (valve, not compressor). :eek:

Hope that answers your Q. :D
 

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Roger said:
im not sure if i have to much or to little to be honest, and i cant really get a good pressure reading. I think im just gonna drain all of it and fill it up according to ounces. How many onces of oil/ r134 or required?
Remember venting the refrigerant is illegal.

Once you get it evcuated, pull a vacuum - very important and fill will 8oz of oil and 26.5 oz of R-134a.

You won't be able to get 26.5oz of R-134a, just pump in 2 cans (24oz).
 

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When you pull a vacuum, the pressure is dropped so that the water in the system is turned to vapour and that can be sucked out by a vacuum pump, along with any air in the system). I am told you can rent these at Autozone in the US.

Peep this - you have air in your system.
There will be water molecules in the air.
What happens when you mix water and cold temps .... ice cubes.
You could possibly clog your system with ice.
This would cause poor cooling, cycling and may eventually build up pressures and blow the relief valve.
 
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