Restriction Before The Drier
Note: Click here for 3 related training videos (Located at the end of this article)
Now that you have accurately diagnosed the issue with the sealed system, click the below button for Sealed System Repair Contents:
With a Restriction before the drier the Low Side Gauge will be reading lower than normal, and the High Side Gauge will also be Reading lower than normal (in most cases high side will be reading 0PSI or vacuum depending on how bad the restriction is). Amp Draw and Voltage will be lower than normal. There will be no to very little frost pattern depending on exact location of the restriction.
The closer the restriction is to the compressor the higher the low side pressure will be. Here is how your gauges could look depending on how close the restriction is to the compressor:
Think about where you are connected to the system with your gauges. Because the Restriction is located before the drier your High Side Pressure will read much lower than normal or even 0PSI.
The Common places these Restrictions occur are shown above with Red Dots.
– The Outlet of the Condenser where it connects to the Yoder
– The Yoder Loop
– Where the steel line connects to the drier
The above 3 Restriction points will show the same result on the gauges. This is because there is enough room for the compressor to push all the refrigerant into the condenser coil which is now acting as a storage tank. So, your low side will be in a deep vacuum and your high side will be very low to 0PSI.
If the system is Restricted closer to the compressor (as indicated with Red Stars above) then you will see a different result. These type restrictions would be:
– At the Compressor to Discharge Line Connection
– In the Discharge Line
– In the Beginning to middle of the Condenser Coil
Restrictions in these areas will cause extra strain on the compressor because it cannot push the refrigerant past itself. Key Indicators: You will often hear the compressor straining, see increased Amp Draw, Increased Voltage, Compressor turning off, and 6 Blink Codes.
Below is an example of what your pressures would look like if the restriction is located close to the compressor:
RESTRICTION REMOVAL
Once you have identified the location of the restriction you will want to isolate the restricted portion of tubing and flush the restriction out of the system. (If the restriction is found in a replaceable part of the system it is sometimes easier to replace the part than it is flush the restriction out). The below illustration shows how to connect your equipment and hoses to flush the system.
Remember when you flush with liquid refrigerant it will need to be recovered.
200 psi is acceptable against the whole system, and 300 psi when the yoder or capillary tubes are isolated by themselves.
Because of the check valve in a dual evaporator unit, only the fresh food side can be back flushed from the suction line at the compressor.
If there is sludgy oil causing your restriction it likely will not blow out right away. In some cases you may need to leave pressure against the restriction for several minutes (we have seen 15-30min in some cases). Once you establish flow with nitrogen then complete with a refrigerant flush.
*Note: Do not damage your gauges when pressurizing with nitrogen. For Example: If your Low Side gauge only goes to 120PSI and you want to pressurize to 200PSI simply use your High Side Gauge only which should allow for the higher pressures.
Below Example is the same unit flushed with only nitrogen first, this is why it is necessary to also flush with liquid refrigerant.
Nitrogen is dry and is very good to push restrictions and most debris out, however the liquid refrigerant will pick up other debris that may be missed by nitrogen, To achieve a clean unit both types of flushing are recommended .
*Reminder: If needing to flush through the 3-Way Valve:
Press the Test Button 1 time
Wait 10-15 Seconds
Unplug Unit from the wall.
This will fully open your 3-Way valve to both sides of the system.
If you find contamination causing restrictions in any section of the sealed system tubing, it is highly recommended to go the extra step and check for a Low Side leak at your evaporator coil(s). Most of the time if there is sludge in the system it is caused by a low side leak allowing moisture in the system and mixing with the compressor oil.
If you do find contamination in the Drier as shown below or in the yoder loop it is recommended to replace the condenser as those contaminants would have traveled through it to make it to the drier and the condenser is likely contaminated as well.
Examples Below:
Restriction at Inlet of Drier Video:
Restriction Removal Procedures:
Now that you have identified the issue with the sealed system and made your repair make sure you achieve a proper vacuum before recharging the unit.
The reason for pulling a deep vacuum is to make sure the system is leak free and all moisture and non-condensables have been removed from the sealed system before recharging the system. This should be performed on every sealed system repair and every time the sealed system is opened for any reason.
The industry standard for a proper vacuum is to reach 500 microns. But don’t stop there…. By monitoring your Micron Gauge you can learn valuable information about the sealed system.
Once you reach 500 microns, isolate the system and micron gauge from the vacuum pump and watch your micron level to see how far it rises. To do this you will need an isolation valve between the vacuum pump and micron gauge:
- Once you have reached 500 microns and isolated your pump what happens next will tell you if you still have issues within the sealed system. It is important that you analyze the micron level for 10-15 minutes after isolating the pump and look for the below conditions…
1) If the micron level rises above 2000 this is an indication that there is still a leak somewhere in the system. Locate the leak, repair, and pull vacuum again.
2) If the micron level stabilizes between 1000-2000 microns this is an indication that there is still moisture/non-condensables in the system. If this occurs, you need to pull your vacuum longer until the micron level stays stable under 1000. (Tip: If there is moisture/non-condensables in the system you can purge the system with nitrogen to clean the system quickly then pull your vacuum again.)
3) The goal to know that you have a leak free and clean system is for your micron level to stabilize below 1000. If you achieve 500 microns and stabilize under 1000 you are good to go ahead and recharge the system like the example below:
Note: If you are having trouble achieving 500 microns make sure your equipment is not the issue. Maintaining your vacuum pump oil, micron gauge, and manifold gauge seals / hoses is very important. If your equipment is in question, try pulling a vacuum on the equipment itself to see if it can achieve and hold proper levels.