AC pressures

[oscarvan]

Two heat pumps are kicking butt. The other two are working but not as they should. Suction side on the former is hot, on the latter is tepid. On the latter what I believe to be the dryer (soup can sized container next to the compressor) is icing slightly.

My limited experience says they're a little low on refrigerant.

Can someone confirm they run on R-22?
And, is there a pressure chart for these anywhere?

I could use the Delta-T method and add small amounts until the output temp matches the good ones, but I'm hesitant to do that because if low refrigerant is NOT the cause it's not good for them. I can also hook up the gauges to the good ones and read them and then hook up to the lazy ones and see what I get.....

Thoughts? (Other than "Call a professional")

Thanks.

 

[Boatsb]

There's a bunch of variables. Liquid pressure and temperature compared to suction pressure and temp on different units can vary. Size and volume matter. Air flow matters. ...

Diagnose each one and make adjustments as needed. Make sure the reversing valves are working correctly. Make sure the water flow and power is good.

If you don't understand the temperature and pressure formulas and superheat calculations bring in a pro and see if you can learn.

FYI. R22 is not cheap or easy to get. Compressors also need oil to run long term. Too much oil is no good. Too much R22 is no good.

 

[kingsley_oasis]

 

[SKYCHENEY]

Yes, original units are R22

 

[oscarvan]

That's awesome. Thank you.

 

[racclarkson@gmail.com]

I have those charts. My AC guy says about 50 psi suction is rule of thumb. Recently I addressed my annual slow leak in master cabin and agree. Given the chart, a bit lower works for me. When I charted the charge, I was close to slugging the compressor. But, my ambients are not yours.

 

[Beachcomber]

I have found them easier to charge in cooling mode than heat mode.

 

[oscarvan]

I have found them easier to charge in cooling mode than heat mode.

That is true for all heat pumps. I'm surviving comfortably in the spaces we most occupy with the other two (aft salon and master stateroom) and a space heater in the galley. So I think I will wait until cooling season.

BTW one of these in the head makes the Admiral VERY happy.

https://www.amazon.com/gp/product/B07XK1R8QT/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

 

[oscarvan]

I have those charts. My AC guy says about 50 psi suction is rule of thumb. Recently I addressed my annual slow leak in master cabin and agree. Given the chart, a bit lower works for me. When I charted the charge, I was close to slugging the compressor. But, my ambients are not yours.

Noted. What were your ambients roughly?

 

[racclarkson@gmail.com]

Noted. What were your ambients roughly?

Seawater 58 F; air temp about 65 F; cabin temp about 70 F. As to delta, also compared compressor head temp and condenser temp with neighboring unit recently repaired.

 

[krush]

Fixed orifice systems, the charge is a little more critical than TXV systems. With that said, if the unit has a slow leak, you don't have to be too perfect on the charge.

The idea of a correct refrigerant charge is to ensure the EVAP gets enough liquid to boil throughout the entire heat exchanger and that there is enough "cold" to cool the compressor.

A down and dirty way to charge these fixed orifice units in summer (and possibly in winter) is to slowly top the charge off until you start getting cold/sweat on the return line to the compressor. You can also feel some cool in the bottom of the compressor, but don't really want the entire compressor to sweat.
Freezing anyway on an A/C system USUSALLY means low pressure due to low charge...but there can be other causes too.

The risk of slugging compressor is possibly, but usually not that great unless you get way stupid and add too much. Put the refrigerant bottle on a scale to get an idea how much you add. The refrigerant enters the bottom of the compressor and cools off the working parts. You'd have to fill the whole housing with liquid before it sucks liquid in the intake and tries to compress it.

 

[oscarvan]

Yes, I use a scale.

Without the gauges and known numbers I use the Delta T method. Works especially well with multiple units as you have a good one for comparison. Measure the air temp at the intake and then at the supply. In cooling mode the difference should be 15º degrees or so, 20º if you're doing really well. Add slowly until it peaks, or in this case until it about matches the good one.

Numbers is better though.

 

[krush]

Do what makes you feel good. Air temp difference across coils is just data, I wouldn't use it to draw conclusions on charge. Grabbing the suction line to the compressor is the best no-gauge charge indicator.