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Refrigerant Oil capacity

By Richard Hawkins, MACS contributor

Editor’s note: The following is a story about refrigerant oil capacity. In my two previous blog articles, we covered how incorrect interpretation of oil capacity information can easily result in the incorrect amount of oil being in a system. As I was completing last week’s article, an interesting tech call that I had had several years ago came to mind. 

The problem the customer was experiencing was excessively high head pressures, elevated low side pressures and poor cooling.

The initial part of the conversation with the technician indicated the following:

  • The vehicle had experienced a catastrophic compressor failure which resulted in a lot of debris in the system and the compressor had been replaced.
  • It was a single expansion valve R-134a system with a 25 oz. refrigerant capacity.
  • The condenser which contained a drier was replaced.
  • The remainder of the system was flushed.

After some discussion on the call about whether the cooling fan was operating properly (and indications were that it was), the conversation turned to refrigerant charge and oil quantity and the conversation went something like this: 

Me:  How much refrigerant did you charge the system with?

Technician:  25 oz, just like the sticker and information says.  I’ve charged it 3 times now just to be sure I didn’t key the information in wrong and the result has been the same each time.

Me:  Are you using new or recycled refrigerant?

Technician:  New.

Me:  It’s very unlikely that a new tank of refrigerant is going to be contaminated but it is possible and contaminated refrigerant can cause the issues you are experiencing.  We need to check and make sure that there isn’t a refrigerant contamination problem here.  Do you have a refrigerant identifier?

Technician:  No I don’t, but we’ve charged 3 or 4 other cars with that same machine from that same tank  of refrigerant and they worked fine.

Me:  OK.  With the A/C systems on those other cars working properly, it sounds like the machine is charging correctly and that tank of refrigerant is pure.  We need to turn our attention to something else.  How much oil does that system have in it?

Technician:  I don’t remember right off the top of my heard because it has been over a week ago since I installed the compressor, but it has whatever the specifications call for.

Me:  Can you  look at the specifications and let me know what they say.  (I had already checked and found out that this system was listed as having a 5 oz. total system oil capacity.  I didn’t mention it because I didn’t want it to have any effect on what he might tell me.)

Technician:  Sure.  Let me pull it up on the computer.

Me:  OK 

Technician:  OK. Here we go. There is this little box that has a bunch of information in it. It says; Total Air Conditioning System: 5.00 oz, Condenser: 1.00 oz, Evaporator:  2.00 oz, Receiver/Drier: 1.00 oz, Line Blown: 1.50 oz, Compressor: Drain and measure the oil from the old compressor, See text.  

Please see the picture below.

This is the box the technician mentioned.

The text says: When an air conditioning system is first assembled, all components (except the compressor) are refrigerant oil free. After the system has been charged with (R-134a) refrigerant and operated, the oil in the compressor is dispersed through the lines and components. The evaporator, condenser, and receiver/ drier will retain a significant amount of oil. Refer to the A/C Component Refrigerant Oil Capacities table.

When a component is replaced, the specified amount of refrigerant oil must be added. When the compressor is replaced, the amount of oil that is retained in the rest of the system must be drained from the replacement compressor. The oil capacity of the system, minus the amount of oil still in the remaining components (refer to the oil capacity chart) can be measured and poured into the suction port of the compressor. When a line or component has ruptured and oil has escaped, the receiver/drier must be replaced along with the ruptured part.

All of that is pretty complicated. It will almost get your head to spinning.  They said that when a component is replaced the specified amount of refrigerant must be replaced.  So I just took the amounts shown and added them up; ( 5+1+2+1+1.5= 10.5).  2 ounces drained from the old compressor, so when you add that in, it comes up to 12.5 oz. The system has right at 12.5 oz in it.

Me:  Well, I think we have found your problem. That system has a huge overcharge of oil in it.  The system has a total system oil capacity of 5.00 ounces.  It is listed on the first line of the box.  With 12.5 ounces, it has a 150% overcharge.  You need to get the extra 7.5 ounces of oil out of that system and it should work fine.

Technician:  I’m frustrated.  I tried to follow the directions and look what happened. They are just too complicated and confusing.

Me: You are exactly right. The way they are written leaves a lot to be desired. What they are talking about is known as oil balancing. That applies to a system that has some oil in it, such as if you were replacing only a compressor because of a seal leak for example.   When you have a dry system like that (no oil in it due to component replacement and flushing) you just need to ensure that the compressor contains the full system oil charge and rotate it about 12 times after installation and you are set as far as oil is concerned.

Technician:  Thanks for the information. I will remember that.

Me: You’re welcome. Please let me know how things turn out.

I’m sure that there are a lot of people reading this who are shaking their heads saying: how could someone make an error like this?  But it happens.  This was an inexperienced technician that just didn’t fully understand some information that could have been written in a much better manner.

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3 responses to “Refrigerant Oil capacity”

  1. Johnny Lawson says:

    I have been searching for this information for weeks. I have a civic all ready to rebuild the entire system but have been waiting till I knew for sure how much oil I needed to put in. People at dealerships and local shops have told me a range of amounts from 4oz to 7.5oz and most said its not that important. I guess that’s true since they didn’t pay for all these parts. Thanks for putting this out there im glad I found it.

  2. David Kent says:

    I have miss placed my certification card. I was certified at a Vintage Air seminar in San Antonio several years ago. How can I get it replaced?

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