View Full Version : Drier Position

22-06-2001, 03:55 AM
For all you guys out there that service smaller systems which employ capillary tubes...

Installing a drier in the wrong position can mimic an undercharged system or a partially restricted drier or even the capillary tube itself. Remember capillary tube refrigeration systems are critically charged... so with that...

HOW can it mimic this? If the drier is installed vertically the liquid is at the bottom of the drier and "vapor" is being passed through the outlet starving the evaporator and causing low suction pressures. Even though the charge is correct the mass flow through the compressor has dropped. Another sign of this would be high liquid subcooling again from loss of flow. In some systems it will be much more noticable, for some the drier cannot even be level but "must" have the outlet pointed down to insure a proper liquid seal at the captube.

Advice: always have your liquid line drier outlet lower than the its inlet and you are less likely to have multiple call backs and a system that is grossly overcharged. If you have a system that seems to require far more refrigerant than the data specs and operates as it should sporadically ... start looking for modifications, drier position is one modification that is overlooked 99% of the time. A system with this drier position modification will often be referenced by one or more technicians as being a "manufacturing issue" and being a poor engineering design.

This is a very typical mistake made in the field as all service techs try to improve a unit from the way they found it, its a matter of pride. Often on small systems there is very little room to place a new drier especially if it is not the OEM drier, so they mount it vertically. And darned if it don't look REAL GOOD standing there too! LOL!!

24-06-2001, 12:02 AM
I take your point about tidy driers Dean, I've done it myself and then thought DOH!

As we tend to change spun cap tube driers with small can driers, 3cu.ins or so could I pose this question?

Assuming that there is limited space for the new, larger, drier would it make sense to make off the cap tube into a section of larger diameter tube which connects with the new drier. This tube could be a bulge or mini receiver and would allow a liquid seal after the drier. It should also allow you to position the drier in a serviceable position without upsetting the cap tube.

24-06-2001, 12:33 AM
This probably sounds like a smart crack... but .... if you have room to install this added "bulge" type receiver, why not just put the drier on its side with a slope to it? I think I am following your question right. I do add a short length of copper tubing to the outlet of the drier and pinch it around the captube then solder it shut.

Sometimes it is easier to make a small loop in your line before the drier, solder it where it is easy to perform then manipulate the tubing and the drier into the desired sloped position... usually I just slowly and gently spread/uncoil the loop and the drier will naturally end up in the correct position. Then lay what is left of the loop sideways if there is room.

I am not sure I described it well, did that make sense?


26-06-2001, 12:14 AM
Originally posted by subzero*psia
This probably sounds like a smart crack... but .... if you have room to install this added "bulge" type receiver, why not just put the drier on its side with a slope to it Yes, point taken, obvious now that I reflect on it. :o

I am not sure I described it well, did that make sense? Yes perfect description, I know when I'm being told off! I would understand it on a cellphone with the van window open at 55, LOL

Prof Sporlan
26-06-2001, 12:50 AM
With a new system install, conventional wisdom is to install a filter-drier in the liquid line and a suction filter in the suction line. The idea here is to keep pressure drop in the suction line to a minimum, as it has a direct affect on compressor efficiency, and suction line filter is less "restrictive" than a filter-drier and provides the necessary protection from system debris for the compressor.

With a compressor burnout, however, placing a filter-drier in the suction line normally becomes the preferred choice. Unlike the suction filter, the filter-drier can remove acids resulting from the burnout which can affect the life of the new compressor. In effect, you are trading a small loss in compressor efficiency with improved operational life of the replacement compressor.

With systems using capillary tubes or orifices, however, care must be exercised when installing a filter-drier in the liquid line. As previously noted, these systems are critically charged, and they cannot have a filter-drier acting as a functional receiver present in their liquid line. Having the filter-drier sloped downward is a good idea. But the Prof might suggest it is safer to place the filter-drier (being properly sized of course) in the suction line where it will be less likely to trap sufficient liquid to cause problems, even if the system isn't being serviced for a compressor burnout.

26-06-2001, 02:55 AM
Please tell me you are talking about a suction drier, and that it MUST be removed within 72 hours after startup.

You have no idea how many suction driers I have seen and or heard of being left in the suction line ... found only after another compressor burnout. I have talked to so many techs that would tell me it was a factory component too... LOL!! Kinda reminds me of when I come across several driers in series and they can't figure out why the system is failed.

If all else fails... add another drier... yeah thats it, thats the ticket! LOL!! (joke!)


Prof Sporlan
26-06-2001, 02:57 PM
Please tell me you are talking about a suction drier, and that it MUST be removed within 72 hours after startup.

Conventional wisdom also states that a suction filter-drier should be removed when it has finished cleaning up the system, and 72 hours after startup is a good rule. :)

But with your typical residential a/c or heat pump service call in which a compressor or condensing unit is replaced, how often will the service tech make a second trip to remove the suction filter-drier? Or for that matter, what homeowner would want to pay the service tech to make that second trip? In too many cases, a filter-drier is not even installed. The Prof believes the economics of selling, installing, and servicing residential a/c and heat pump systems makes for less than ideal service practice. Installing a properly sized suction filter-drier and leaving it in the system is still significantly better than not installing a filter-drier at all. At least the compressor will remain clean as it struggles to remove Btus... :)

The Prof agrees the suction filter-drier should be removed from the system when it is no longer necessary, and this practice is better observed with refrigeration and larger a/c systems where reduced compressor efficiencies can present greater problems, and the service tech normally has more time to do things correctly.

26-06-2001, 11:13 PM
Whilst in total agreement with previous comments especially the Profs' on small a/c equipment. It isn't just the customer who won't pay the extra it can also be your Guvnor who doesn't see the need for the return visit - but that's another matter.

I appreciate the need to monitor the pressure drop across a filter after a cleanup but was wondering - does anyone make an acid indicating sightglass, or similar, that could be temporarily fitted along with the filter? Or would this gizmo be a non-starter?

23-07-2001, 10:28 PM
Brought a small water chiller into the workshop today for a compressor swap - major electrical failure somewhere had blown the capacitors, strat relay etc (sorry - another story...)

Anyway took off the covers for access and saw a capillary installation that would please everyone ;) , short stub of pipe off the condenser, 90 bend to the vertical, cap-line drier in the vertical with the cap-line rising from it.

I'm still trying to figure out where the liquid seal could be hiding :D

I think a little modification could be in order before I return this one.