Issues with HPC

[jdbradley]

I have been working on a good friend of mines 3 year old Armstrong heat pump the past couple of evenings and boy has it been a good one. The first day i showed up and found the compressor had shorted out causing a funky burnout, i go to the supply house the next day and pick up the warranty compressor and get it installed. Purged the lines, installed a new bi-flow liquid line drier, triple evacuated the system and dumped the factory recommended 410a charge into the system. Fired the compressor up and got equal pressures on the discharge and suction lines. Reversing valve was bad, come back the next day and put the dreaded reversing valve in the was also under warranty, triple evacuated, charged it back up. Fired the system up again everything is running good in cooling, adjusted the charge to 15* subcooling, 12* superheat, everything is looking good. Started packing my tools up in the truck and i told by buddy i wanted to check heat mode, compressor fired up and kicked out on high pressure within 10 seconds. I know i have a blockage in the system somewhere and i am pretty sure it is the condensing unit TXV, its the only thing that makes sense to me. I just wanted to run it by you guys to make sure i am not missing anything so i do not have to break the bad news to my buddy for the 4th time. Thanks in advance.

[Kevin Weaver]

So you weighted in the factory charge. Great. Then you say you adjusted it to superheat and sub-cool. Is the indoor metering device a txv? When I hear "adjusted the charge" to me that means you added charge. You could be over charged. Or you don't have good indoor air flow. 15 Subcool is a little high. Is the indoor unit properly matched? When I am working on a heat pump, I turn it on in the A/C mode, then when I need to check it in heat, I disconnect the orange wire only. If this is dual fuel, maybe the gas furnace was on?

It very well could be the txv. Usually the low side pumps down when this happens.

[jdbradley]

The evaporator has a non adjustable TXV on it, the condenser and evaporator coils are clean, 15* sub cooling is the factory recommendation. I doubt there are airflow issues since the system was running perfectly in cooling. I am curious as to what else can cause a blockage in a heat pump system in heat mode and not in cool.

[timebuilder]

The evaporator has a non adjustable TXV on it, the condenser and evaporator coils are clean, 15* sub cooling is the factory recommendation. I doubt there are airflow issues since the system was running perfectly in cooling. I am curious as to what else can cause a blockage in a heat pump system in heat mode and not in cool.

Heat mode? How about the outdoor metering device?

[jdbradley]

That is what i am thinking, i was just curious if anyone else has run into this issue. I have never had a burnout create this much havoc in a heat pump before.

[fitzyfitta]

Is the condenser a micro-channel?

[fitzyfitta]

What's the make and model of the unit.

[brian.cornell]

Is this a matched system and the air handler installed at the same time as the heat pump? If not I bet its overcharged even if you weighed it in by the nameplate.

[jtrammel]

Sounds like overcharged to me, maybe low id airflow too.

[techonsite]

all your txv's job to do is maintain superheat somewhere between 8-15 As long as it has saturated liquid coming into it. It sounds like your txv is doing its job. Check airflow.

[mason]

I've seen units charged to 12-15* subcool trip in heat mode on high pressure. If indoor temp is at the normal levels of comfort I'll only go up to 8*, unless other factors like long line set or vertical pressure loss are issues.

Get a subcool measurement in heat mode, see what it does before it trips.

[jdbradley]

Thanks for the replies. It does not have micro channel coils, it is a matching Armstrong setup, the condensing unit is an Armstrong 4SHP13LE136P-1 serial is 1609F00406. I checked the evaporator coil which was in pretty good shape, put a new filter in it. The reason i was leaning towards the external TXV is, this unit is equipped with the TXV's with internal bypass. An overcharge does make sense, the data plate says the factory charge is 10lbs 2 oz which does seem a little high for a 3 ton unit with about 15' of line set. I will pull some of the charge out and bring it down to 5 degrees or so of subcooling and see if it will run in heat before i change out the expansion valve. Thanks for the help, this is a great site!

[mason]

Let us know how it turns out.

Get your post count over 15 and apply for pro membership, one of the best things you can do to be a better tech is get into the locked pro forum.

[jdbradley]

Well it was not the expansion valve but I have found the reasoning behind this. I called the factory for some support, gave them the model and serial of the condensing unit and air handler. They told me the air handler was for AC only, so the evap coil is way undersized which makes a lot of sense. I am sure this is the reason the compressor failed because it has been kicking out on high pressure for 3 winters. Makes me angry that someone would do something like this but i am sure it happens every day out there. Thanks for the help on this one, it has been a learning experience.

[BNME8EZ]

Were you running in cooling then switched it right into heat or was there some down time inbetween? Just a thought, if the outdoor coil is hot and it goes directly into heating your throwing hot gas into a hot coil and pressures will rise rapidly.

[jdbradley]

It goes through the 5 minute compressor delay then the reversing valve energizes equalizing the pressures. I dont think that would be an issue. What kind of size difference are we talking about on an AC vs heat pump evap coil? I have never really paid attention.

[pony]

so did u change the coil for heatpump?and did that solve the problem?