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Originally Posted by MicahWes

I always thought the evaporator would use LESS refrigerant when the box is near design temp. There is less load, TXV throttles, less liquid refrigerant present in coil.

Think a little harder about it.

At the lowest load, the superheat is the lowest.

Lower superheat means more liquid lying in the evaporator

More liquid in the evaporator.....

Originally Posted by Dchappa21

Yep add the flooding charge after the glass is full AND system is almost at set point.

Your evap coil will use much more refrigerant as it get cold, as less refrigerant is boil off and the coil is more flooded..... Unless your TXV is grossly oversized.

I always thought the evaporator would use LESS refrigerant when the box is near design temp. There is less load, TXV throttles, less liquid refrigerant present in coil.

I agree. I'm printing this out and keeping it in my truck.

Thanks all for the advice.

Originally Posted by markettech

Attachment 321041

In looking at the above figure, the following may explain why you were seeing bubbles in the sight glass.

As the system head pressure falls below the set point of the headmaster, the valve starts to modulate - closing off port C and opening port R by the same ratio. This results in refrigerant backing up in the condenser as discharge gas begins diverting directly into the receiver.

Conversely, as the head pressure hits the set point of the headmaster, the valve starts to modulate once again - opening port C and closing port R by the same ratio....resulting in increased flow of refrigerant through the condenser into the receiver and restricting discharge gas from dumping directly into the receiver.

More than likely while you were adding refrigerant to the system, the discharge pressure temporarily exceeded the headmaster set point and therefore refrigerant was not allowed to stack in the condenser - so your system was sufficiently charged.....briefly.

Once you stopped adding refrigerant and the system was allowed to stabilize, the head pressure most likely dropped below the headmaster set point and refrigerant started stacking up in the condenser - and where you barely had enough refrigerant in the system before, now there simply isn't enough of a charge to both stack in the condenser and maintain a liquid level in the receiver.

Start adding refrigerant again and the cycle repeats.....until such time there is enough of a charge to allow the headmaster to do its job and form a liquid seal at the outlet of the receiver.

If you spend some time studying the figure and reflecting on how subcooling is derived, it should also become readily apparent as to why charging by subcooling simply is not an effective way to determine an acceptable system refrigerant charge.

I haven't clicked on JPSmith's link, but I would imagine he is directing you to Sporlan's step-by-step procedure for properly charging a system such as the one you are working on.

Very well said, I think I even understand it a bit better now.

Originally Posted by markettech

Attachment 321041


I haven't clicked on JPSmith's link, but I would imagine he is directing you to Sporlan's step-by-step procedure for properly charging a system such as the one you are working on.

Attachment 321041

In looking at the above figure, the following may explain why you were seeing bubbles in the sight glass.

As the system head pressure falls below the set point of the headmaster, the valve starts to modulate - closing off port C and opening port R by the same ratio. This results in refrigerant backing up in the condenser as discharge gas begins diverting directly into the receiver.

Conversely, as the head pressure hits the set point of the headmaster, the valve starts to modulate once again - opening port C and closing port R by the same ratio....resulting in increased flow of refrigerant through the condenser into the receiver and restricting discharge gas from dumping directly into the receiver.

More than likely while you were adding refrigerant to the system, the discharge pressure temporarily exceeded the headmaster set point and therefore refrigerant was not allowed to stack in the condenser - so your system was sufficiently charged.....briefly.

Once you stopped adding refrigerant and the system was allowed to stabilize, the head pressure most likely dropped below the headmaster set point and refrigerant started stacking up in the condenser - and where you barely had enough refrigerant in the system before, now there simply isn't enough of a charge to both stack in the condenser and maintain a liquid level in the receiver.

Start adding refrigerant again and the cycle repeats.....until such time there is enough of a charge to allow the headmaster to do its job and form a liquid seal at the outlet of the receiver.

If you spend some time studying the figure and reflecting on how subcooling is derived, it should also become readily apparent as to why charging by subcooling simply is not an effective way to determine an acceptable system refrigerant charge.

I haven't clicked on JPSmith's link, but I would imagine he is directing you to Sporlan's step-by-step procedure for properly charging a system such as the one you are working on.

Originally Posted by Phase Loss

I usually just add refrigerant until the compressor starts to rumble. That way I know I'm slightly over charged. Then block the condenser and let the auto reset pressure relief pop off, once it resets, your system should be correctly charged.

This reminds me of a dude that used to work where I do before I got there. The old supervisor tells a story of him soon a tune up on a 5 ton rheem split where he knuckled in the contactor and was watching the suction pressure. Of course it didn't go up so he adds refer. Keeps adding it until the compressor locks up, somewhere in the neighborhood of 30 lbs. Come to find out he didn't turn the air handler on. Lol.

Originally Posted by Phase Loss

I usually just add refrigerant until the compressor starts to rumble. That way I know I'm slightly over charged. Then block the condenser and let the auto reset pressure relief pop off, once it resets, your system should be correctly charged.

LMFAO... That's one way to add the winter charge... I bet there is actually somebody that out there that does this.

Originally Posted by 54885488

One should never use subcooling with a receiver in a system ? I did not know that .

You can use it all you want... But it's not going to change after you fill the sight glass, unless you fill the receiver full of liquid and start to stack refrigerant in the condenser.

Originally Posted by Phase Loss

I usually just add refrigerant until the compressor starts to rumble. That way I know I'm slightly over charged. Then block the condenser and let the auto reset pressure relief pop off, once it resets, your system should be correctly charged.

Lol.

I usually just add refrigerant until the compressor starts to rumble. That way I know I'm slightly over charged. Then block the condenser and let the auto reset pressure relief pop off, once it resets, your system should be correctly charged.

One should never use subcooling with a receiver in a system ? I did not know that .

Originally Posted by Dchappa21

Wrong... Forget subcooling when you have a receiver. Subcooling is what it is just fill the glass and add winter charge if needed.

^^
Love to hear the eh cooling explanation though.

Originally Posted by Tommy knocker

Stop by first thing in the morning. If temp is below 60 or so and glass is clear your probably ok. Good luck

Actually, I misinterpreted this post.

I would go by the charging guidelines from the manufacturer or Sporlan (in that order)

http://sporlanonline.com/90-30-1_072012.pdf

I use this for charging systems with a headmaster control.

If you've got a receiver in the system, charging to subcooling is a no-no. It won't work for you.

Originally Posted by Kevin_1963

This looks like my answer. My receiver is the size of the refrigerant tank. There's not enough info on the condensing unit to get an accurate manufacturer - and the charge amount was written in sharpie, so it's not the first time its been serviced. For all I know, the 33lb could be low. It has a headmaster, and the rooftop temp at the time was 72. I wish I could've gotten the head pressure, but by then the guy had pulled the hi side off and was charging low side. Yeah, I shoulda put a high side gauge on and confirmed pressures, but by then we were wrapping up. Anyways, today I called and they told me the unit was still down in temp, but one these days I'm gonna go back and double check everything.

Lesson learned - do your own follow ups, and if you can't, make sure the guy following up is doing it right.

Stop by first thing in the morning. If temp is below 60 or so and glass is clear your probably ok. Good luck

Originally Posted by Tommy knocker

Your still low. Like already pointed out you should have a good sized receiver. If its warm out your glass will fill but receiver will be empty so when headmaster starts throttling all your liquid gets stacked in cond coil and glass will start flashing. You can, and I would pull the charge and weigh it back in. Or keep guessing at it and give yourself grey hair. That's where mine came from.

This looks like my answer. My receiver is the size of the refrigerant tank. There's not enough info on the condensing unit to get an accurate manufacturer - and the charge amount was written in sharpie, so it's not the first time its been serviced. For all I know, the 33lb could be low. It has a headmaster, and the rooftop temp at the time was 72. I wish I could've gotten the head pressure, but by then the guy had pulled the hi side off and was charging low side. Yeah, I shoulda put a high side gauge on and confirmed pressures, but by then we were wrapping up. Anyways, today I called and they told me the unit was still down in temp, but one these days I'm gonna go back and double check everything.

Lesson learned - do your own follow ups, and if you can't, make sure the guy following up is doing it right.

I know a lot of times when charging a large system, the sight glass gets clear and then will start bubbling again. I charge through the low side, and flash off the refrigerant in my gauges as a liquid, let the compressor pull it in. As it gets through the condenser and receiver, the sight glass will show a solid column of liquid for a little bit, and then once more vapor gets back to the compressor, it will show more bubbles. Just keep an eye on it and see, if you didn't find any leaks, chances are there isn't a leak that large.

I would agree with you on a cap tube unit or a system with no receiver subcooling needs to be checked for proper charge through.

Originally Posted by keviekev70

Forget the sightglass, charge by subcooling it's to only way to tell if the system is fully charged.
I use the sight glass for the moisture indication only.

Wrong... Forget subcooling when you have a receiver. Subcooling is what it is just fill the glass and add winter charge if needed.