Normal range of superheat and subcool for auto A/C systems?

Leggie on Thu October 24, 2013 4:34 AM

Under ordinary test conditions. If taking SH at closest point from the evaporator suction line and SC at the end of condenser, what are some reasonable ranges?

iceman2555 on Thu October 24, 2013 9:10 AM

The SH of the evaporator is controlled by the TXV. The TXV's have a numeric value stamped on the case, most later model vehicles are around 3-5 degrees SH. The typical temperature drop across a condenser should be around 18-20 degrees min. However, we have experienced vehicles with properly operating systems with slightly less temp drops. A typical Parallel flow condenser should experience a temp drop of 23-28 degrees. A sub cooling parallel flow condenser we have experienced temp drops as great as 48 degrees. One must know exactly what type condenser is being tested to determine these conditions. Also most of our testing is conducted under high head loads. Max cool, high blower, cabin doors open, engine at idle speed. Increasing cabin cooling by closing the doors and or elevating engine rpm may change this values.

These are great tools for a post repair/performance evaluation of a system, however, one must know the validity of the testing tool. Since the hand held infrared or laser appear to be the most common, it is suggested that these tools may not be the best tools to utilize. Testing under various conditions and different 'guns' we have discovered that temps may vary as much as 75-80 degrees. Should one wish to move into temperature testing, it is highly advised that a very good electronic thermometer utilizing thermo probes be utilized. Also keep in mind that the location point of testing is important also. Test as close to the inlet/outlet as possible and away from as much under hood temps as possible.

One should also keep in mind that all temperature/pressure indicators are only valid for a fully charged system. Pressures ARE NOT and indication of a fully charged system and temperatures are only valid for a fully charged system. Changes in charge rate can and will effect both. It is essential that the system be properly charged utilizing the correct measuring equipment. Attempting to charge to a particular pressure/temperature range is not a suggested or proper method to insure proper charge rates.

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The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

wptski on Thu October 24, 2013 10:50 AM

Not sure how correct they are but there are a number of videos online showing HVAC techs adding/subtracting from a charge to increase/decrease SC/SH values.

HECAT on Thu October 24, 2013 12:18 PM

Its works for HVAC work because baselines (compressor RPM, air flow, etc.) are much more consistent than with MVAC

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wptski on Thu October 24, 2013 2:11 PM

The newer A/C units in HVAC are marked with SC and SH values from the manufacturers.

iceman2555 on Thu October 24, 2013 7:38 PM

A suggestion would not be to follow HVAC SH/SC procedures for automotive AC charging...adding or removing....charge the vehicle utilizing the correct equipment. Use temps for performance evaluations etc...but not to determine a true charge rate. An exception would be the evap inlet and outlet temps of a orifice tube system. Our testing has always conducted under high heat load conditions. Closing the cabin may invalidate results.

Hey, guess what, the Europeans are 'playing' with another new refrigerant....not HFO1234yf...but a new blend of one of the 1234 gases and CO2. Recovery machines are in the 15k range. More about this 'CF' at a later date.

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The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

wptski on Thu October 24, 2013 7:50 PM

Is that R744 that you are referring to? R744.com

iceman2555 on Thu October 24, 2013 8:38 PM

No...the new refrigerant is a blend of one of the HFO1234 cousins and 744 (CO2). The goal of the European market is to drive customers back to the dealerships for all service procedures. The complexity of this new gas and the equipment necessary to recover, what gases need to be added to the mix and recharge this mind boggling. There are a lot of questions concerning 1234yf and many mfg'ers are backing away from it's use. Appears to be just another government boondoggle that results in mass confusion and the expenditure of major amounts of cash. Heck about 25% of the shops in the US today do not have the correct equipment to properly service todays AC systems...and now we are possibility adding a refrigerant that must be recovered and blended in the shop prior to use.....give me a break.....let the EU do as they please....let's stay with 134a.

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The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

wptski on Thu October 24, 2013 9:16 PM

Yeah, in Germany they sold vehicles with R134A that were by law to have HFO1234yf. They were trying to force them to recall those vehicles.

HECAT on Fri October 25, 2013 11:18 AM

AC5 and AC6 refrigerants

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