How much PAG oil to add when replacing compressor according to experts

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Below we answer one of the most common questions we get: How much PAG oil to add when replacing compressor

A common question that we come across from people who have just replaced the ac compressors on their cars is “how much PAG oil to add when replacing compressor?”

So here is exactly how much PAG oil you should add in the new compressor…

How much PAG oil to add when replacing compressor (how much PAG 46 oil to add to compressor) to avoid cooling issues

In general, any time you’re replacing a compressor, you need to do something called oil balancing- and this procedure is what will tell you how much PAG oil to add.

In a nutshell, oil balancing is simply draining out your old compressor then measuring how much oil comes out.

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Next, drain your new compressor then add back into it the same exact amount of PAG oil that had come out of your old compressor (you obviously want to refill the new AC compressor with new oil -and not the old oil you had drained from the old one).

For example, if the broken compressor you have removed contained 3 ounces, the replacement compressor should be refilled with 3 ounces too.

This way, you maintain the original ounces of oil – remember the objective is to maintain the OEM amount (oil charge needs to be consistent with your new system).

In short, this is the safest way to determine the accurate amount of oil you’ll need to put in.


What happens if I add too much PAG oil?

Too much oil typically restricts flow through the condenser – condenser tube passages are quite small so overfilling it greatly hampers the flow of refrigerant through the tubes.


What happens if I add too little PAG oil?

Too little oil will, on the other hand, decrease lubrication- if you get just an ounce (or two) less in there, cooling will definitely start to be affected at some point.

That is why oil balancing is so important- not too much and again not too little should go in there!


Do you need to add oil to a used AC compressor?

Well, if you have picked an AC compressor from a junkyard, here is what you should do to be safe:

Turn the compressor (on its side) and check if oil comes out.

If yes, go ahead and measure how much will come out (you will empty out all the remaining oil and measure it).

This is what you will, once more, need to add (Be sure to always use correct viscosity PAG oil!). 


How often should I be replacing the AC compressor in my car?

AC compressors are not parts that will need frequent replacement in a vehicle.

The truth is, you will only need to replace it very rarely- and not every 40,000 miles.

In fact, if you find that you have to frequently replace it, the problem is likely to be elsewhere (think an accessory drive belt that is misaligned, a defective pulley creating undue stress, or something else).


Car AC compressor failure symptoms

So, how do you tell if your AC compressor has failed?

Here are some common car AC compressor failure symptoms..

  • The AC compressor is barely spinning when your car is on- it’s really struggling
  • Some grinding noise- Bad bearings (in the compressor) usually causes noise (sort of a grinding noise) so loud noise can signal compressor failure.
  • If your AC compressor is locked up completely, the belt is likely to just be grinding (on the pulley) and therefore smoking / burning.
  • Cold air tends to go away when you are sitting at stop lights or idle.
  • Clutch not moving- Another symptom of a troubled compressor is clutch not moving.
  • Worn compressor belts- if you’re noticing physical wear (or damage) to compressor belts, then it could indicate a failing compressor. You may also inspect the compressor itself for any visible signs of wearing (it could mean it’s bad).

If any of the above has been happening, probably it’s time to replace the compressor (you want to perform a comprehensive diagnosis before that because it’s an expensive repair and you want to be certain it’s the compressor)


Can I drive my car without AC compressor?

As a temporary resolution -until you can afford the AC repair- you can cut out the belt system drive and still drive the car just fine (You want to unplug the AC compressor so that it won’t kick on).

Keep in mind that, you can as well install an AC bypass pulley- for some vehicles- if you’re never going to use the AC in your vehicle again (if that’s the way you’d like to go).


AC compressor replacement tips

  • Oil and the refrigerant are different hence you should ensure the lines (in your manifold) have been flushed. In addition, if your old compressor died, it’s best to also flush the system.
  • Check for “black death”- If the cause of the compressor failure is piston failure, you may want to inspect the lines for black death (broken pistons often release tiny black particles into the AC system- and these end up circulating throughout the system).
  • Check the inlet and outlet during compressor removal- Swab with a Q-tip (swab both). If they come up green or clear, you should be clear to proceed. But if either comes up black, there might be trouble ahead.


How much PAG oil to add when replacing compressor – Recap

To determine the accurate amount you’ll need to put in, drain out the oil from your old compressor then measure it.

You should then drain the replacement compressor and put back in the exact equal amount that had come out of your old compressor.

Do new AC compressors come with oil? We answer

AC compressor low oil symptoms – The telltale signs

How to flush AC system with alcohol


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