Heat pump problem

[lexscripta]

Went to a call on an old TRANE unit that has the TXV in the condenser. Low cooling, high head 30-40psi suction. Plenty of refrigerant in the system, good airflow at Evaporator and at Condenser.

Not real familiar with heat pumps, I wonder if someone can answer this -

What are the issues that can cause high head and low suction in a heat pump other than a liquid line restriction?

I have a liquid line drier and there is no temp drop across it. I have a suction line drier with shraeder ports on either side and there is no pressure drop across it. The TXV in the evaporator has the distributors making ice, so my guess is the TXV has a restriction.

So anyhow - is there something else in a heat pump that can cause high head / low suction pressures, ice build up on the evaporator distributor in a TXV sys?

[The Viking]

To answer your question:
The most common reason for a high head pressure in a heat pump would be a restricted airflow through the "indoor" coil.

This however, wouldn't cause a low suction pressure or the outdoor unit to ice up.

To get a better idea of what is going on more information is needed, for starters;
-condenser air on / air off temperatures
-evaporator air on / air off temperatures
-subcooling
-superheat

[lexscripta]

Please note:

"Went to a call on an old TRANE unit that has the TXV in the condenser. Low cooling, high head 30-40psi suction. Plenty of refrigerant in the system, good airflow at Evaporator and at Condenser."

Ok, so thats not the issue - how about some others. I am looking for what could be the cause. For exammple, can the outdoor TXV cause something like this? The reversing valve?

Remember, its abnormally high head and abnormally low suction.

[Gary]

Went to a call on an old TRANE unit that has the TXV in the condenser. Low cooling, high head 30-40psi suction. Plenty of refrigerant in the system, good airflow at Evaporator and at Condenser.

We can't see it from here, so we need a better description.

High head doesn't tell us anything, because it is an opinion, not a high side pressure.

30-40 psi suction? Is it 30 psi or is it 40 psi?

And pressures don't tell us anything if we don't know what refrigerant is in the system.

Plenty of refrigerant is an opinion. What is the subcooling? What is the superheat?

Good airflow is an opinion. What are the in/out air temperatures for both coils?

And on a heatpump it is confusing to call the coils condenser and evaporator. Call them indoor coil and outdoor coil.

I assume it is in cooling mode.

[Brian_UK]

The TXV in the condenser unit will not be used in cooling mode.

[lexscripta]

We can't see it from here, so we need a better description.

Ok, guess I was looking for generalities. You know, what can cause low pressure in an R22 heat pump. Its running about 35 psi in cooling mode. 320 PSI on a 90 degree day.

Obviously, there is a problem just from the pressures alone.

Again, just generalities. What can cause a situation like this?

We have these possible scenarios that could cause it:

1) Low airflow across inside coil in (cooling mode)

2) restricted liquid line, txv, drier...

What else can it be in a heat pump? A assume Not a restriction in the TXV in the outdoor coil because its in cooling mode.

Can a partially restricted bypass valve cause this?

Thanks

[lexscripta]

The TXV in the condenser unit will not be used in cooling mode.

Thats what I thought!!! Thanks!

[Gary]

The high side pressure problem is caused by insufficient airflow or overcharge or non-condensibles.

The low side pressure problem is caused by insufficient airflow or undercharge or restriction.

My guess would be that the TXV inlet screen or drier is restricted and someone dumped a lot of refrigerant in there in an effort to compensate for the low side pressure... but that's just a guess.

[lexscripta]

Thanks,

That's the sort of thing I was looking for. Since I am not familiar with heat pumps, I wanted to make sure that I wasn't overlooking some other possibilities.

[lexscripta]

BY the way, I'll report back in a few days with the readings, including SH and SC readings, if it will help.

As to air flow, I am assuming everything was alright before the issue occurred, I looked at the indoor coil, and indeed 2 problems were at issue - the belt was loose, and part of the insulation fell down onto the inlet side of the coil. However, fixing these two problems only gave me about 5 PSI increase on the low side guages.

If there is a restriction in the liquid line drier, would I not expect a temp drop across it? What about the suction drier?

The suction drier has inlet and outlet shraeder ports. No pressure drop across there either.

BY the way, this TXV is brazed in - do they have inlet screens that can be cleaned?