New heat pump install shuts off on high limit

solradman

Just installed a 3 ton heat pump with matching indoor coil on a down flow gas furnace for a duel fuel system. Turned on power to heat pump and set t-stat up a couple degrees to start system. Heat pump control show call for heat and waiting for anti short cycle period before starting. After time delay period unit starts and high side starts build pressure at steady rate all the way up till high limit shuts it down in about 30 seconds. (625 psi) Low side steady at 125 to 130 psi. Have checked furnace speed and removed air filter, both are OK. Each time unit does the same thing.

Line set is 10 feet long with no kinks. Suction line has 6 elbows, liquid line all one piece with long radius bends. Did install an indoor TXV and removed all caps and dirt seals before installing. Did double evac to 300 micons and used nitrogen during brazing and to break first vacuum.

Any help on best way to figure out what is causing this.

Ironman

Not enough info. It could be any of several causes.

My first question would be are you a licensed HVAC contractor or tech?
Second: do you know and understand the refrigeration cycle?

JUGHNE

Is the HP coil on top or bottom of the down flow furnace?
What is the outside temp?
Was the gas furnace firing with it?

AMservices

Does the high limit trip running in cooling? Do you have a by-flow filter dryer? Are you using long sweep elbows?

njtommy

Is the Gas Furnace on at the same time?

solradman

I've included some pictures to help answer questions. Ironman: you were right, not enough info so guess I deserve some of these questions. Answer to yours: yes and yes. Jughne: look at the pictures, around 50 degrees and no, the furnace is not running at the same time. AM: Did not try it in cooling, best question asked, and Fraser-Johnson states a "liquid line filter dryer is factory installed to protect the compressor against moisture and debris" so one would think it is by-flow. All turns are long radius in both lines. njtommy: see above.

This was an add-on system to an existing gas furnace. The home owner wanted AC and I recommended the heat pump to save on the heating costs which is one of the reasons we got the job. The home is 3 years old and this is the third furnace they've had installed but that another story. It had a sheet metal box under it for an add-on coil and we had to take it all down to put a taller cased coil in and then put it all back together. Finished installation late Friday afternoon and was hoping all would be good when we turned it on so did not have much time to do a lot of trouble shooting.

newagedawn

sounds like a low voltage wiring issue, if you installed A/C the high limit switch souldnt be an issue?

Ironman

I would try it in cooling with the OD temp at least 70*.

Your info is still a little vague, but here are some thoughts:
1. Did you remove the piston from the ID coil?
2. Did you add or remove any refrigerant?
3. What's the model of the HP & ID coil?
4. How many cfm are you moving across the ID coil?

Ironman

newagedawn said:

sounds like a low voltage wiring issue, if you installed A/C the high limit switch souldnt be an issue?

I believe he's referring to the high pressure control.

JUGHNE

Three year old house with this the 3rd furnace......maybe a serious ductwork problem.
What happened to the first furnaces?
You could just operate the gas furnace to see if it has been cycling on limit.....could be a quick check of air flow.

njtommy

Definitely sounds like an air flow issue. Why 3 furnaces in 3 years? That's very odd.

njtommy

Also looking at your install I would lifted that furnace off that A coil 6" and transition to it down to allow air flow to hit it evenly.

AMservices

Was the TXV a match for the coil or did you use a universal one that would have to be braised in place?
That to me would be the more likely suspect. Some manufacturer is set the install are up for failure by mounting the TX valve directly on the other side of where your brazing.
It doesn't sound like an air flow problem if the unit short Cycles within the first 60 Seconds.
You can diagnose the airflow by checking the temperature rise across the coil. Probably looking for a 20 to 30 degree delta T on a 60 degree day.
The fan speed should always be on high with a heat pump, should have 1200 CFM with 3 ton capacity.
You can check the TX valve with the cup of ice water and a cup of hot water, by dunking the temperature sensing bulb ( one cup at a time) and watching your gauges for the fluctuation.
If the TX valve is stuck closed that will show it.

JUGHNE

Is the inside TXV designed for heat pump use? That is as in a flow/check which would allow the liquid to flow back out to the outside unit? Does it work OK as an AC?

solradman

And the winner is , "stuck TXV". Tried sticking the bulb in the ice and hot water with no change in operation from before. Next, thinking that something might have gotten in during assemble so sucked it down and opened it up. Could not find anything inside and a nitrogen purge blew through with ease. Had picked up another TXV from the supply house so installed it, did a pressure test and a double suck down. Weighted 80% of charge back in and turned it on and away it went. Did a final adjustment to the charge per manufactures charging chart and its working nicely. Just need to wait for a warm day to try AC. This stuff always happens on Fridays.

OK, the story of the three furnaces, as I have heard and understand it. If another heating guy would have told me this I would think they made it up, but I saw it myself.

This is a spec home built in a neighborhood with 50 or so others around the same size. Only a few companies do new construction installations in our area and it seems they over size everything. The rest of us do not want to play in that game. First furnace was an 80 percent 80,000 Btu 4 ton unit according to permit app. In the Great Northwest (Go Hawks) we like crawl spaces and that's were ductwork goes. I figure the installer are not the sharpest and do not know the difference between an upflow or downflow furnace, or they just installed whatever was loaded up for them. In this case an upflow and it made all the way through the building and buying of the home until the new owners needed heat and the warm air was coming out the returns.

Was told the same company came out and switched out the furnace with a 100,000 Btu/ 4 ton downflow model. That's number 2. Guessing they did not want to buy a correctly sized unit so they put in what ever they had in stock and would fit the base and top cans. FYI, I ran 3 heat loss with an average load of 36,382 Btu's at 21 degrees and 31,118 for cooling at 95 degrees. We get that warm sometimes. I would have recommended a 60,000 Btu/3 ton furnace.

This is where it was when I came in for an AC bid on a referral. I like duel fuel with gas and a heat pump over gas and AC and tell people the energy savings will pay the difference in a few years. However, I told them the new furnace was way oversized and had to go. That's when I heard the story. It was a battle to get this across to them and I do heat loss /gains on all jobs. We have a really great official state energy website with heat loss/gains and cost comparison apps for people to do themselves which really helped with their understanding in this case.

I suggested they call the installing company for an AC quote. Have them do a heat loss/ heat gain on the home, then ask them how they could justify the 100,000 Btu furnace. I have not ask if they did, however I got a call 2 weeks later and was told they got a new furnace. That's number 3, an 80 percent, 80,000 Btu 4 ton. Again, I can only figure the company did not want to put in a properly sized one because they would have needed to change out the top and bottom cans. You know, It's all about the bucks.

What do we hear all the time, do it right the first time...

Thanks everyone for your help.

Harvey Ramer

Is that a Fraser Johnson HP?

Ironman

'And the winner is , "stuck TXV".

I doubt that was your problem if nitrogen passed through. Even if the powerhead was bad, or the valve failed to open, that would not effect the OD unit in the heating mode. Only a stuck internal check valve would have caused that since the TXV's cage is bypassed during the heat mode.

Maybe it was over charged?

ChrisJ

Harvey Ramer

Ironman said:

'And the winner is , "stuck TXV".

I doubt that was your problem if nitrogen passed through. Even if the powerhead was bad, or the valve failed to open, that would not effect the OD unit in the heating mode. Only a stuck internal check valve would have caused that since the TXV's cage is bypassed during the heat mode.

Maybe it was over charged?

I'm thinking down the same lines.
If it is a Fraser Johnson, the indoor TXV is a Sporlan RZ series with Chatlef fittings. I have never seen one of those checks stuck in a new valve. If the piston was installed it would exhibit the symptoms he described. As well as an overcharge.

And why weigh in 80% charge and then do the rest with your guages? Especially with brand new equipment designed for and using 410-A. Thats a good way to get the system overcharged, especially in this weather. And if it is a Johnson Controls unit, they don't supply charging charts for heat mode, not to my knowledge. Plus, they invariably show low condenser pressure on a new install. That has tripped up more than a few folks with good intentions. The best way by far is to weigh in the correct charge, as calculated by the manufacturer instructions.

JUGHNE

I had a heat pump work in the heating mode but in AC mode it would just pump down as if it were low on charge. Turns out the TXV was plugged but the bypass would work for heating. The brand of Txv/coil had a history of problems.
I am very over the top with N2 and triple vac to the point of ridiculous. Something about oil in coil or compressor oil.
They just gave me a new coil w/TXV.

I have always assumed that if the subcooling charge is correct for AC then it would be good for heating? How wrong am I?

Harvey Ramer

> @JUGHNE said:
> I had a heat pump work in the heating mode but in AC mode it would just pump down as if it were low on charge. Turns out the TXV was plugged but the bypass would work for heating. The brand of Txv/coil had a history of problems.
> I am very over the top with N2 and triple vac to the point of ridiculous. Something about oil in coil or compressor oil.
> They just gave me a new coil w/TXV.
>
> I have always assumed that if the subcooling charge is correct for AC then it would be good for heating? How wrong am I?

A lot of the new HP's I see and install, have suction line accumulaters. They aren't very sensitive to charge in cooling mode, but very sensitive in heating. Very very easy to get overcharged if using the charts instead of weighing in.

Ironman

I've seen as little as 3 ounces make the head pressure skyrocket on a 3ton unit with a mini tube coil.

Some may disagree, but I think the manufacturers have sold us a bill of goods with these micro channel and mini tube coils.

AMservices

@solradman
Happy to hear you solved the problem.
Just wondering, did you test it in cooling before diagnosing TXV?
If so, did you see the restriction?
Your gauges tell you everything about Refrigeration system. If the compressor is running, you know the piping is correct, airflow is correct, the next thing to show a restriction would have to be metering device at either one of the two coils.
There have been a couple of times when I've replaced the TXV and still found the restriction.
The manufacturer then warranties me the coil and that's the end of it.
I completely agree that these micro Channel coils are going to be big problems.
You would think the smaller tubing and needing twice as many loops, it would give a higher pressure drop through the coil. And because there are so many more connections, there is that much more of a chance for a leak.
I was unaware of check valves in these heat pump systems.
I always thought that because the TXV is taking temperature and pressure, when the valve sees a high pressure and temperature it would fully open. Then you have a TXV on both coils for when their roles are reversed.
I guess I'll find one the hard way someday.

ratio

IDK about mini tube coils, but the microchannel coils I've come across have been parallel, not lots of passes. Once through the condenser section, then once through the subcooler section. I wouldn't be surprised if total pressure drop went down. Still not much volume, but they've been producing radiators for many years now, I expect the microchannel coils to be fairly reliable once they get their minds around the metallurgical change from Cu to Al.

One of these times I'm going to saw open a header to see how they get the in plug that separates the sections. From a quick glance, they're cast in one piece.

solradman

Sorry, poor or wrong choice of words. Something stuck in it or one of the line could or may be better. I tried the unit in AC with the same result. The Fraser Johnson support people asked if we had removed the all the protection covers that came on the valve during shipping. I could not be a 100% sure that one had been missed during assembly or something being in the 3/8" line as it comes in a coil and you can not see though it. I pulled the first TXV and purge nitrogen though both lines to clear them, valve not in place. With the nitrogen tank set up outside I was not able to see if anything came out of the lines the first couple seconds of purging.

In the past I've always weighting in a heat pump charge, figuring the unit charge, then add or subtract for the line set. However the manual states that the system charge will cover the outdoor unit, 15 feet of line set and the smallest indoor coil match up, what about an oversized coil?. Called FJ support to see how much to take out for a 10 foot line set, answer was 3 oz's and that even more may need to come out and try putting in 80% and adjust it from there. Page 7 of the installation manual under "Charging the Unit" states "on new system installations, charge the system per tubular data sheet for the matched coil." "Table 6: YhbE 35 Heat Charging Chart." is found on page 10 of the Fraser Johnson HP Installation Manual. With 80% charged into the unit it started and ran without going into lockout and I finished adjusted the charge per the chart and will see how that works.

The system is running very will in heating with the new TXV and using their charge by chart method. It's going to be in the high 70';s tomorrow so may be I can see how it works in AC. Where it would be interesting to see with the new TXV installed, by adding the full system charge it would result in an over charged unit and a high pressure lockout, for now I think I will go with I screwed it up the first time around.

Thanks to all.

solradman

Correction, Table 7 THE/HP 14L36