high compressor discharge

[trennick]

I confess that I am not an expert in HVAC, more of a general ME, so I'd like your help. Can anyone give me a list of possible causes for higher than expected compressor discharge pressures on a refrigeration system?

Causes that come to my mind are:

1. Refrigeration overcharge
2. Too much oil in compressor
3. Restrictions in the piping (where might these be?)
4. ???

Are there any other candidates? Are the ones I've listed strong candidates? What might be the most likely cause? Any good published sources that I could refer to?

Thanks for any help,
Tim

 

[MintJulep]

Non-condensable gas (like air) in the system.

Dirty condenser coils.

 

[waross]

Is this a new system or are the high pressures something that has developed in a previously good system?
yours

 

[pennpoint]

High condensing temperatures.
Sun shining on receiver.
Undersized receiver.
Filter-drier clogged.
TXV or capillary tube clogged.





Best regards
pennpoint

 

[HVAC68]

Other causes could be

1. Condenser fan not running.
2. Discharge shut off valve partially closed.
3. Non-matching indoor/outdoor combination ?

HVAC68

 

[quark]

Malfunctioning discharge valve plates.

Most unlikely, discharge isolation valve malfunctioning.

 

[imok2]

Pennpoint, I feel I must correct you on the following answers:

High condensing temperatures do not necesseraly increase head pressure. With refrigerant undercharge you will have low head pressure but hi discharge temperature. This is the same as a clogged drier, restriction in liquid line defective TXV bulb, high superheat,etc.

Sun shining on receiver will deminish sub cooling and may increase flash gas thereby decreasing mass flow and deminishing refrigeration effect,this in effct will inrease superheat which will increase discharge temperatures but decrease head pressure. (mass flow)

Undersized receiver should have no effect on head pressure as long as the proper amount of refrigerant is in the system, in fact you can eliminate a receiver if you maintain the proper amount of refrigerant in the system as is done in a cap tube system

Filter-drier clogged will deminish mass flow and result in less gas pumped, this will result in a lower head pressure and a higher discharge temperature because of increased superheat

TXV or capillary tube clogged will result as same as above.

Quark, malfunctioning valves will deminish efficiency of the compressor and lower both head pressure and temperature.

Discharge isolation valve malfunctioning will deminish mass flow and reduce head pressure but may increase discharge temperature because of some re-expansion of the discharge gas as the total volume may not clear the cylinder.

 

[MintJulep]

Sun shining on receiver will deminish sub cooling

I'm not sure I follow you here. If you have a receiver then you have no sub-cooling, since the refrigerant must be at saturation in the receiver.

Unless you mean that the saturation pressure of the refrigerant in the receiver will be higher, and therefore the performance of any subcooler downstream will be proportionally reduced

 

[pennpoint]

imok2
Go ahead, and Good on you. I should have waited for the OP to reply to "waross" post, which was on point. When DID this occur...

Mass Flow eh! I'll be...






Best regards
pennpoint

 

[bukac1]

Check temperature on the discharge pipe close to the compressor. Then consult tables of the properties of the refrigerant the compressor works with. If the table shows the condensing (saturated vapor)pressure is the same or close to the pressure you measured, then problem is high consensing temperature because the condenser is unsufficiently cooled.

 

[imok2]

MintJulep, You are correct: "If you have a receiver then you have no sub-cooling, since the refrigerant must be at saturation in the receiver".
What I didn't say was that in many cases you would need to sub-cool the refrigerant after it left the receiver other wise the slightest pressure drop would flash the refrigerant. I thank you for the oversight :>)

 

[Skogsgurra]

I am sure glad not to be in this business. Had no idea that my old refrigerator could have sooo many problems. I will treat it more respectfully in the future.

Gunnar Englund

http://www.gke.org

 

[imok2]

Gunner, Problems are what most of us love, especially if we can solve them or collarborate with others to find a solution :>)

 

[tbedford]

The type of system and compressor would be of some help.

High pressure can also be caused by non-condensibles or contaminants (wrong refrigerant).
An under-sized receiver or condensor can cause high pressure.
High ambient conditions or dirty condensor or low water/air flow...or high water temp.
Service valve partly closed.

Tom