Check The Charge Without Gauges – Podcast

In this episode of the podcast, we talk about gauges. Jim Bergmann from Redfish Instruments and the MeasureQuick app gives us all a detailed explanation of how to check a charge without using a gauge manifold. (That's not clickbait; if you've already connected gauges to a unit once, you can probably check the charge of that unit WITHOUT gauges moving forward.)

HVAC units manipulate temperature and pressure in the refrigerant charge. Heat transfer occurs between the refrigerant and the environment, and various readings indicate the charge level WITHOUT necessarily connecting the gauges. So, you can check the charge if you know the unit's SEER rating, target superheat, DTD, CTOA, and if the unit uses a fixed orifice or TXV.

A large portion of checking the charge without gauges deals with “benchmarking” the equipment. You do that by evaluating the system's performance over time and comparing it to the performance when the system was first commissioned. Airflow WILL decrease over time due to components becoming dirty.

You can check the charge without gauges if you use the following process (and know your DTD, CTOA, etc.):

  1. Take the dry-bulb temperature. (Let's say it's 70°F in this example.)
  2. Subtract the DTD (35°F).
  3. Add target superheat (10°F).
  4. Check the suction line. It should be 45°F in this example. If your probe senses a temperature that is NOT within 5°F of the temperature you calculated, check the filter, evaporator coil, etc., for dirt.
  5. If the system is not dirty, check the charge with gauges.

For a more extensive look at the process in writing, check out THIS article.

Bryan and Jim also talk about:

  • Heat transfer
  • Educational books (Refrigeration and Air Conditioning Technology)
  • SEER variations
  • Dirty equipment
  • Suction line insulation
  • Various superheat readings
  • Uncertainty of measurement instruments when determining DTD and target subcooling
  • Condenser sizing

If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.


Justin Jedidiah Lawton
Justin Jedidiah Lawton
6/19/17 at 02:10 PM

If this is the kind of stuff you are teaching your own to do Id like to work for you. Great stuff.

Joe Reinhard
Joe Reinhard
6/26/17 at 11:44 AM

Bryan, Jim, Super informative and convincing discussion for very, very infrequently installing gauges if not only once.
Definitely on-board with using benchmark DTDs, SLTs, SH, LLTs, SC, and ESPs readings done during first-ever system assessment and new system startup which should not change during the life of the system unless one or more of the following developed:
1. Air flow restriction
2. Component failure
3. Refrigerant flow restriction.
I also reviewed Chap 40 in Refrig & Technology big book and made more sense this time.
Having listened to both podcasts several times, I developed a Word file of benefits, “Data to record” first-time visit or new system commissioning, “data to record” for follow-up maint checkups, and other notes.
If you’d be interested, I would like to email to you for review for accuracy and edit suggestions. Fine to share with Jim if desired.
Appreciate yours and Jim’s humor and respect for one another. I felt “your pain” several times during Jim’s good-natured question grilling.
That “pain” somewhat resembles pressure I feel when encounter system problems w/out apparent or clear explanations. Inclined to start grasping (“gasping”) for info and data readings when only usually need to not over-think and look at simple causes & reasons.
Thanks for your time investment and committment to and helping others become better technicians. P.S. Thanks for the TTTools coupon.

Romer Zerpa
Romer Zerpa
2/6/22 at 09:14 AM

Chapter full of Science and simple principles that are going in a fast and pushy way into our brains.
Repeating the whole thing is a must.
Thank you for providing/promoting free education.

Colin Densmore
Colin Densmore
6/25/22 at 02:02 PM

Great information. I cannot stress enough how informative your overall platform is. I have been listening/reading since the beginning. I am a Journeyperson of 5 years and continue to read the tech tips/listen to the podcast, forever learning!

Douglas Rodger
Douglas Rodger
3/30/23 at 01:20 PM

Great stuff, I enjoy how individuals like you and Jim continue to provide useful information for techs of all ages and abilities to use. You should always be a life long learner. Never settle in, this industry is always changing. You have to keep up by education. Keep up the good work.



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