Heat Pump Gauge Use.
I know it is late in the cold season, but I swear I have hardly had any
heat pump calls until these past three weeks. Now pretty much every
call is a heat pump. It is causing me great stress.
I have been reading a bunch of heat pump threads and trying to gleen info,
but I'm almost out of weekend time for this weekend--I have other tasks
I need to do today.
So my questions are about putting gauges on a heat pump in
heat pump mode. I don't because I have absolutely no clue
what they would tell me. Even in low ambient, I put in a/c mode
and then will maybe check SH/SC if pressures aren't really obvious.
I have come across the two semi-accepted heat pump charge checking
#1 Hot gas: Adding 110 to your outdoor air and checking that against the discharge line temp.
I am guessing that lower means too little refrigerant, higher is overcharged.
#2 Un-named: (Ambient DB +20) times .4=temp rise indoors (at air-handler?)
I'm assuming that lower rise means undercharged, and higher rise means run back
to your van. Ha, ha.
But then I see this third schraeder valve on a lot of heat pumps and I have to
believe that it is meant to be used. I believe it is tied to the inlet of the compressor
close to the reversing valve? (I have not actually checked that on a unit, just gathered
it from my reading.)
So my question is simply whether I should actually put on gauges in heat
mode, whether I should ALWAYS use that third port, and what can pressures/sat temps
Thank you all.
Easiest charging method I've seen is the first one you mentioned. Hot gas, 110F + OAT = Discharge temp. This will put you "in the ball park"
Other people will say the only way to charge a heat pump is to reclaim and weigh it in according to manufacture specs, but my boss would tell me that takes too long.
The third port is your dedicated suction/low side port, it connects into the refrigeration circuit before the reversing valve.
Your high side hose goes to the discharge line (larger of the two lines in the lineset)
On a Trane HP, pull off the side panel and the ports are on the reversing valve. Discharge is on top by itself, suction is in the middle on the bottom.
Hope this helps you out a little.
Most units have some kinda of chart for checking the charge in heat mode, only one that i havent seen any type of charts inside the panel were Goodman.
Other than Carrier type units, hook your high side like normal, on the liquid line valve because thats always going to be liquid, and like earlier stated, use the common port. On Carriers, they meter outside right before the liquid line service valve with a piston.
I know what you mean. The last two weeks I've had at least one hp service call a day, and on days where I wouldn't have one, the next day I would have too. My service manager laughed when he heard this and said "You're going to become our new heat pump guy whether you like it or not." I don't mind, but I would expect to start getting these calls in November, not January.
Originally Posted by georgelass
Find a unit with a chart and take a picture on your cell phone so you can refer back to it. I took a pic of one for 22 and 410. It will get you close. You definitely need to hook your gauges up. A rule of thumb for temp rise that I was taught is at 32*F oat the temp rise will be 20. For every three degrees +/- oat the temp rise will be 1 degree up or down. That is based on proper airflow and proper charge. Dirty coils/ filter and it will definitely change.
Send me an email ( address is in my profile), and I will send you a PDF of how to hook up your gauges and temp probes for heat pumps.
Originally Posted by georgelass
I don't post technical info in this "OPEN" forum.
You have the 110 over ambient backwards. Too low discharge temp is overcharged.
Don't forget its still just a refrigeration system.
Heat pump can be charged in the heating mode using SC & SH. However, if the charge is adjusted in the heating mode, you will need to fine tune it in the cooling mode when spring hits. The system requires more refrigerant in cooling than in heating thats the reason for the accumulator. It's always better to charge with warm OAT and in cooling mode. I would probably go with the weigh in method, keeping in mind length of line set. In either case, charging in heat mode will get you close enough in cooling mode that you should be able to get back in spring to fine tune. (when I hook up to heat pump I always use the liquid line on high side gauge and my low side gauge to the true suction tap regardless of which mode I'm in, just don't want to run in to the situation were I think im going to be using cooling mode and the reversing valve doesnt switch and I destroy my guage). Maybe I'm just paranoid.
Temperature rise is not reliable because it is too dependent on indoor air volume.
Originally Posted by 2141
...seek, and ye shall find;..
So always seek the Truth, not just what you want to believe to be true…
Ecclesiastes 10:2 NIV
The system requires more refrigerant in cooling than in heating thats the reason for the accumulator.
AND i thought the accumulator was to keep liquid from entering the compressor. Pretty sure that the charge level should be the same in heat or cool mode... and please if i am wrong someone plz let me know
[QUOTE=Jkb79;15034721The system requires more refrigerant in cooling than in heating thats the reason for the accumulator.[/QUOTE]
The outdoor coil is much larger than indoor coil. In heat mode, the extra refrigerant required in cool mode has to be stored somewhere, and it's the accumulator.
Originally Posted by SuperTech2010
The accumulator also keeps liquid from flooding the compressor.
Originally Posted by Thermodynamics
Using similar logic (albeit simpler) to the above, if the indoor unit coil was 1 and the outdoor unit coil was 2, then in cooling mode:
2 + 1 = 3
In heating mode:
1 + 2 = 3
In heating mode the outdoor coil is obviously the evaporator and since it is generally larger than the indoor coil the refrigerant by design should be superheated by the time it hits the accumulator, if the system is operating within design conditions of course.