A/C Compressor Oils And Their Effect On Elastomers

© 2018 Eaton. All rights reserved..

A/C Compressor Oils And Their Effect On Elastomers

Aaron D. Clark M.S

Eaton Corporation

© 2018 Eaton. All rights reserved.. 2

Overview

This presentation covers a detailed study examining the compatibility between common elastomeric materials and relevant compressor lubricants using quantitative processes. The objective is to characterize suitable materials for mobile A/C applications and aid the designer with selection and troubleshooting.

3© 2018 Eaton. All rights reserved..

Agenda

• Purpose Statement

• Causes of A/C Failure

• Mechanism of Chemical Compatibility

• Test Fluids and Materials

• Data

• Conclusions


Common Causes of AC Failure• Dirty Coils or Corrosion

• Blocked/damaged Suction Lines

• Low or Overcharge of Refrigerant

• (Electrical Problems)

• Hose and Seal/O-Ring Related

• Inadequate Oil Lubrication – Loss of refrigerant resulting in poor oil circulation and reduced lubrication for the compressor

• Moisture - Degradation of a hose or seal allowing moisture to enter the system, mix with the refrigerant and form an acid.


The Dangers of Low Refrigerant• Reduced System Performance

• Icing - If there is insufficient refrigerant inside the evaporator coil, the coil will lose its heat absorption ability and condensation in the system will freeze causing heat exchange to cease.

• Compressor Failure -The loss of refrigerant will cause a compressor to potentially overheat and eventually burn-out.

Compressor motor extreme failure


Fluid Compatibility - Hose

• Incompatible fluids can make the hose assembly swell, shrink, blister, deteriorate and delaminate


Causes of O-Ring Failures:• Design Related• Material Related

• Abrasion• Chemical Compatibility• Compression Set• Extrusion• Spiral failure• Thermal capability• Weathering

• Installation Related• Production Quality Related

Fluid Compatibility - O-Rings & Seals

• Material swell and loss of properties may lead to o-rings & seals becoming susceptible to mechanical degradation and failure during use, especially in dynamic applications.


O-Ring/Seal Failure Modeso Extrusion Failure :

• Seal material migrates between the mating surfaces.

o Compression Set :• Rubber compounds can permanently deform under strain which decreases sealing force

resulting in leakage• Compression set is the percentage of deflection that the elastomer fails to recover after a

fixed period of time under a specific squeeze and temperature.


Factors Influencing Chemical Compatibility

• Polymer Related:

• Plasticizer and filler type and content:

• Crystallinity and Cross link Density

• System Related:

• Temperature & Pressure: Diffusive rates increased by a factor of about 1.6 for every 5 degree increment.

• Fluid Related:

• Molecular Weight : Inverse relationship to diffusive uptake. Relates to Viscosity

• Solubility : Hansen Solubility Parameters characterize the interactions between an elastomer and a fluid by estimating the relative miscibility of polar and hydrogen bonding systems.


Mechanism of Fluid Compatibility

Solution-Diffusion Model (Thomas Graham, 1866) –Permeants dissolve in a material and then diffuse through the membrane acrossa concentration gradient

Two steps:1. Adsorption or adherence of the fluid

onto the surface of the solid based on solubility.

2. Diffusion through the channels in the polymer interstitial space along a concentration gradient (Fick’s Law) from highto low concentration

R’ I

RO-(CH2-CH-O)n-R”


Mechanism of Fluid Incompatibility

Once inside the interstitial space

• Swelling/shrinking of the elastomer

• Plasticization of the polymer strands

• Loss of physical properties

• Chemical attack on the polymer

Exposure to Fluids

Time/Temperature

Diffusive Uptake

Higher Conc. Lower Conc.


Chemical Degradation

• Abstraction of a tertiary hydrogen atom from the polymer chain as a result of oxidation.

• The hydroperoxide that forms can cycle and abstract another hydrogen until bond scission occurs.

+ RHeat/O2

+ ROOH

ROOH RO + OHHeat

+ RO

Type 1: Hydrogen Abstraction from an Alkane Bond


Chemical Degradation

• Rupture of pi bond leads to formation of a carbonyl (aldehydes and ketones)

Type 2: Oxidation of an Alkene Bond

Type 3: Deterioration of Cross Links:

O2/Heat

O2


Chemical Compatibility Testing

Chemical Compatibility Rating

Testing:• Oil Exposure - ASTM D471• Physical Properties - ASTM D412• C Set – ASTM D395

Worst Case Scenario Testing


o Polyalkylene Glycol (PAG): Pro: Good hydrolytic stability Pro: Burns cleanly without generating residue Pro: Acceptable with R-134a and R-1234yf Con: Absorbs water Con: Not compatible with PAO and Mineral Oil

o Polyolester (POE):• Pro: Compatible with Mineral Oils and PAO Pro: Acceptable with R-134a Mandatory for hybrid electric systems Con: Absorbs moisture Con: Can generate sludge Con: Hydrolytically unstable at high temperatures Con: Acceptability in R-1234yf TBD

Refrigerant Oils


o Polyvinyl ether (PVE) –• Pro: Good hydrolytic stability• Pro: Good compatibility with other oils• Pro: Better than POE for R-410a• Pro: Compatible with R-134a• Con: Acceptability in R-1234yf TBD

o Polyalphaolefin (PAO) -• Pro: Good hydrolytic stability • Pro: Compatible with Mineral Oils and POE• Pro: Low moisture absorption• Con: Can form deposits when used at high temperatures• Con: Acceptability in R-1234yf TBD

Refrigerant Oils


Refrigerant Oils - Composition

Refrigerant Oil Requirements:• Good anti-wear / lubricity• Low foam and rapid air release• Low pour point• Low floc point• Good chemical / thermal stability• Compatibility with rubber & plastic

components• Compatibility with refrigerants• Prevention of acid, sludge, rust and

deposit formation.


Materials Studied

EPDM Polyamide (PA)

Acrylonitrile (NBR) Butyl (IIR)

Chloroprene (CR)

Polymer Temperature Capability Application

Acrylonitrile (NBR) -40°C to 125°C Hoses/Seals

Chloroprene (CR) -30°C to 100°C Hoses/Seals

Butyl (IIR) -50°C to 125°C Hoses/Seals

EPDM -50°C to 150°C Hoses/Seals

Polyamide -40°C to 140°C Hoses


Study 1: Fluid Type vs. Polymer Tensile Strength

• Total test time is 168 hours @ 100°C


Study 1: Fluid Type vs. Polymer Elongation



Study 1: Fluid Type vs. Polymer Volume Swell



Study 2: Effects of Time on POE Volume Swell

40%

• Test temperature is 100°C


Study 3: PAG Oil Comparison

• Materials studied include CR and Polyamide• Various PAG 46 type oils tested from different manufacturers• Total test time is 168 hours @ 100°C


Study 4: Oil Viscosity Study

• PAG oils with 46, 100 and 150 viscosities examined.• Total test time is 168 hours @ 100°C


Rubber Formulations Vary!


Study 5: Formula Variance vs. Compatibility • 2 Chloroprene recipes were examined that varied 25% in total filler content.• The exposure was 168 hour immersion in PAG oil @ 100°C

Low Cost Standard


Standard Practice -ASTM D2000 “Call Out”

© 2018 Eaton. All rights reserved.. 28

Conclusions

• Quantifiable variation exists in material response to refrigerant oils

• Oil Viscosity does have a minor effect on material properties

• Significant differences in oil formulations exist between products and can generate mixed results

• Use caution when selecting hose and seal materials to avoid incompatibilities


• “The most common cause of a Refrigerant Leak is due to an O-Ring”• http://xpectmoreautomotive.com/ac-system-and-coolant/• https://aristair.com/blog/8-preventable-causes-of-ac-compressor-failure/• https://www.quora.com/What-causes-a-car%E2%80%99s-air-conditioner-hose-to-start-leaking-from-the-

crimped-fitting• http://blog.parker.com/top-8-reasons-hydraulic-hoses-fail• Patech; http://slideplayer.com/slide/1425457/• https://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=2250&context=icec• http://www.hydraulicspneumatics.com/hose-tubing/guide-recognizing-causes-hose-failure• http://flodynamix.com/o-ring-failure-chart.html• https://www.bimmerforums.com/forum/showthread.php?1226116-catch-can-install-gt-oil-leak-around-

dipstick• http://www.brianb.org/images/Scuba/Homemade/Gas%20Booster/gas_booster.htm

References


Acknowledgements

• Chris Seeton• Derrick Craddock• Doris Showalter• Gina Clark• Karl Myers• Keith Swearingen• Matt Sexauer


Documents

A/C Compressor Oils And Their Effect On Elastomers