High head - low suction

I'm new here, but a seasoned tech. To me I would be looking at your new coil. If the sensing bulb is not placed correctly, it will royally screw things up. Second, it is not uncommon to have a new, defective TXV. I have ran into it several times. Check the liquid line temp before and after the metering device. Check your delta "T" at the indoor coil. Make sure the house is not lacking return air(Very common in old houses), make sure the customers furniture is not restricting the return air grills upstairs. I would be checking different parts of the system with your thermometer. Ensure the fan is set at the proper cfm. In my opinion. it's always best to start at the basics. Hope this helps. :cheers:

 

Sound like you have a restriction in the system. Verify your airflow and check the TXV if used with the new coil if not piston maybe clogged, check temp across filter drier, look for an unintentional kink in lineset after the new coil was installed.

 

Despite what the customer says, you have to investigate a restriction. Did someone install a new LL dryer, or forget to change an old dryer because it is hidden in the OD unit?

If the customer insists he is correct, you'll have to walk away.

 

This is a classic sign of a partial restriction that we argue about here around once a year. It goes against what we're taught but even with the proper charge it will cause extremely high head pressure. It obviously has to be down stream from wherever you're reading the high pressure. If you're reading is on the liquid line then the indoor coil would have nothing to do with it. The most common place would be the metering device or screen at the outside unit but as suggested it could also be a plugged dryer but that's pretty unlikely.

 

My bad,

I read the OP wrong, I thought it was fine in cooling but high head in heating so disregard this post. I'll have to read it over again.
I'd still be looking at a restriction with those pressures but a little more info is needed about both cycles.

 

Pony,

You've posted problems like this before and have always been asked for the same information.

Pressures alone don't mean anything.

What is the superheat? What is the subcooling? What is your indoor airflow?

Start taking a more comprehensive set of readings when you have a trouble system and you will find more problems, faster.


Anyone posting a solution is doing little more than guessing without more data.

 

went to customer home check on r22 heat pump cut out ,the pressure on high side is 400 lbs,and low side is 30 lbs in cooling mode,and it run 3mins and cut off each time u turn it on,and running in heat mode the pressure is normal,but still cut off in few mins,check the line voltage is normal,condenser coil is clean,indoor coil in new with tev,and running in heat or cool mode the suction line get correct temp(hot and cold real fast),he already have two tech come look at it,cant find out what is wrong,i think is new indoor coil restriction,or even system have more then one problemmaybe air in the system,but customer said it is new cant be!what do ur thinks?thanks

A cold suction line (low superheat) with low suction pressure is a symptom of low evaporator air. A liquid restriction would result high superheat (warm suction line). The high head probably due to the other guys overcharging, trying to get the suction pressure up.

But the low air problem would result in high head pressure in the heat cycle.

If the contactor is actually dropping out, I would guess a hi/lo pressure limit opening.

 

Winner winner chicken dinner..................:cheers:

Your unit has been severely overcharged, pump it out, pump it down, then fill er back up.................................then find the restriction.

 

new coil does it has a 410-a txv or was it changed to a r-22 valve

 

3 mins of runtime will not allow you to get an accurate superheat/subcooling reading so giving a solution to first correct the problem (3mins then cut off) is more than just guessing, then checking superheat/subcooling to specs to properly charge the system. Pressure alone in this instance is more than enough info. Come on now!!!

 

Iszell

Read the OP's other posts.

It is my opinion that he has no business touching an HVAC system beyond the thermostat.

 

Pony,

Did you determine why it "cuts off"?

One would ASSUME high pressure, but assumptions are not part of good service practices.

A new coils doesn't mean that you have good indoor airflow. This is why an airflow test is required.

You state condenser coil is clean. Did you clean it or are we still assuming?

And even with 3 minutes of runtime, you'll know if the superheat is high or low.

 

any body think maybe compressor trip cause it have running with low freon for long time,maybe mechanicaly falier in compressor over heat and trip?that is one more thing i have to check amp draw from compressor,cause i am looking at the liquid line restruction and high and low pressure to long,lol,

 

If you replace the compressor it still won't solve your pressure problem. You've got some good advice already on where to look. Solve that & I'll bet all will become clear.

 

If you knew your superheat then you would know if it's getting proper cooling for the compressors sake.

 

:deadhorse:

 

Haven't heard anything about a possible reversing valve issue? The complaint suggested the unit trips in both cooling & heating mode. Maybe a restriction is present there or the pilot operator is not functioning right? But ultimately, readings with a pipe thermometer at all points of the system may shed light. As suggested, superheat and sub cooling are also critical (if you have sufficient run time to measure these).

 

you no understand English? You speak

When I see paragraphs such as shown above, I can't help but wonder if all of those run-on characters, shifting syntax, and poor spelling aren't a symptom of simply not being familiar with the language.

 

Try recovering all freon weighing what recovered see if weight matches name plate now you have system open you can orfices put new drier in visual inspect all copper lines with the unit trippin l.p and h.p switches it might be hard to check temp diff throughout unit im not the best tec but some times just starting over brings the end to the beginning.

 

I was just goona say the same thing.

Hey timebuilder you reading this? L

 

Not enough info Pony Provide make and model of heat pump and indoor coil. You stated indoor coil is new was the size verified as a match with the original heat pump.

Need to provide more information:

Did you verify airflow requirements by TESP or pitot tube traverse?

OAT Temps

Return Air Temps WB and DB
Supply Air Temps WB and DB

Locations of Gauge pressures. Vapor Line Liquid Line True Suction Pressure True Discharge Pressure.

Temp on each RVS line

Temps across filter driers.

Without adequate information one can only guess.

 

HATE THAT! Its the old not enough info $%$. One follows the other. Comp can oly discharges as much as it can receive. I would take an amp reading first.

 

Actually, amperage isn't going to tell us a lot here.

We already know that the suction pressure is low and the head is high. This will lead to a distorted amperage.

 

True! But its better than asking wb and db temps to determine high suction pressure. Wish my bank would work that way. Low money in high money out.

 

It seems to me that about the only thing that will cause the same symptoms in both heat and cool is noncondensibles. Low airflow would cause high head low suction also but having low airflow on both indoor and outdoor units at the same time is pretty slim. Since the evap was just changed noncondensibles seem quit likely since a restriction will normally act like an undercharge if you don't look at SH/SC. So I;m putting my money with the guys that say pump it out and start fresh.

 

A brief observation. This past summer I had to replace a leaking indoor coil. It shipped from Carrier with a new txv. I could barely get the charge in. High head, low suction. Pulled the charge and found the txv 100% closed. New txv, all OK.

Now, you can take from that what you will.

 

A brief observation. This past summer I had to replace a leaking indoor coil. It shipped from Carrier with a new txv. I could barely get the charge in. High head, low suction. Pulled the charge and found the txv 100% closed. New txv, all OK.
Now, you can take from that what you will.

I've gotta ask this.
Are you saying you had high head & low suction and the unit wasn't fully charged?

 

Come on guys relax a bit there is no way in heck you can test a unit if it trips h.p and l.p switches within a few mins so waiting for.more info is out of the question the only option is to start from scratch. Refer back to last post. also when done with everything from last post you blast nitro through liquid line and you dont get any presure reading from suction boom you got.restriction now find it lol

 

Now that I'm home, and not trying to type on a phone, let me give you some additional info. Maybe it will be what you are "wondering."

My account is meant to be elementary, so everyone can learn from it. I also like to use a little sarcasm where appropriate. Perhaps that isn't always understood.

I never said I didn't have guages on. I reported the pressure was high, and that it was high enough to open the switch. Even though I have heard that a lot of this stuff is just plain junk, I wasn't expecting to have to replace parts that had just come out of the box, so I wanted to give the pressures a chance to subside, in case it was a minor issue that was going to clear. Some of that pausing was a sense of disbelief, that here I was, on a hot day, having just come from the Vet where I had to put down my favorite pet, and now I get to climb up in the ceiling and tear open the ill-fitting and clumsily installed box again to replace what SHOULD HAVE BEEN a perfectly good TXV.

It was easy at that point to see that this part was indeed FUBAR right out of the box, and that is an important note about the unit: a Carrier split rigged for the "big lie" refrigerant that they are now talking about replacing.

In an irony, this chain shoe store decided to close that location three months later.

Any questions?

 

I am laughing my butt off as I read

...

I never said I didn't have guages on. I reported the pressure was high, and that it was high enough to open the switch. Even though I have heard that a lot of this stuff is just plain junk, I wasn't expecting to have to replace parts that had just come out of the box, so I wanted to give the pressures a chance to subside, in case it was a minor issue that was going to clear....

Your quote again

...

... so I wanted to give the pressures a chance to subside ....

TO TRIP THE HIGH PRESSURE SAFETY SWITCH???? AND not even look at the subcool.

Come on man! You are smarter than that.

 

Under the right conditions, a LOW charge can cause high pressures.

:.02:

 

Under the right conditions, a LOW charge can cause high pressures.

:.02:

And in fact, it did.

The system may have had high delta T because we do not maintain the systems (it's not our contract for this customer, we do only the on-demand service, and NO installs) and the system was inop on arrival for the no AC call. That's when we ordered the new coil and TXV.

It probably was not condensing very well. That is probably the difference between shutting off a liquid line valve and the bad TXV. On the day the job finished, it was unusually cool and the heat load was substantially lower. It cooled acceptably for a piece of junk.

The new TXV had to be shipped in from Georgia.

That's the bottom line.

IN THIS CASE. :angel:

 

<at timebuilder>

i replaced 2 emerson expansion valves at seperate jobs within the past 2 weeks. Returned to both jobs today to find them failed, yet again. Needless to say both require mt to lay on my stomach in 14" of blown in to replace. I feel your pain.

 

To all tech out there. You can check this condition out yourself. EASILY

IN THE SPRING SEASON or SUMMER SEASON (if you have time).

When you go out to a heatpump system like trane, Lennox that I know it has a DEDICATED high pressure port (port on the discharge line right before the reversing valve). OR any straight cool system that HAS A DEDICATED HIGH PRESSURE SWITCH locating before the liquid shutoff valve.

MAKE SURE

1) The system does not TOO LONG of the line set. 25 - 30 feet are OK.
2) The system is PROPERLY charged.

Put your gauge on this high pressure port and run it on COOL MODE.

NOW close the liquid line service off AND report the high pressure gauge. And you don't have to ask this question again.

My bet is

High pressure will climb just a little bit.
As its suction pressure drops, the compressor is lack of freon to compress. Thus the high pressure drops.

Pennies for your thoughts.

At normal circumstances, how many time we pump the system down and the high pressure switch don't trip. SO what is the difference between shutting off the liquid valve and having stuck-closed TXV ??????

 

To all tech out there. You can check this condition out yourself. EASILY

IN THE SPRING SEASON or SUMMER SEASON (if you have time).

When you go out to a heatpump system like trane, Lennox that I know it has a DEDICATED high pressure port (port on the discharge line right before the reversing valve). OR any straight cool system that HAS A DEDICATED HIGH PRESSURE SWITCH locating before the liquid shutoff valve.

MAKE SURE

1) The system does not TOO LONG of the line set. 25 - 30 feet are OK.
2) The system is PROPERLY charged.

Put your gauge on this high pressure port and run it on COOL MODE.

NOW close the liquid line service off AND report the high pressure gauge. And you don't have to ask this question again.

My bet is

High pressure will climb just a little bit.
As its suction pressure drops, the compressor is lack of freon to compress. Thus the high pressure drops.

I wonder how many time we pump the system down and the high pressure switch don't trip.

How are you supposed to make sure the system is properly charged if you have a restricted TXV? I don't know about you but I don't take the gas out of every system I work on & weigh it to see if my charge is right. If I'm charging an empty system I like to weigh my gas but I still use pressure & temps to get it right in the end. You assume because timebuilder had very high head pressure that he overcharged the system. I assume the opposite, that he couldn't get a full charge in the system because of the bad TXV.