Rheem High Pressure Trips

PaulLambert

Hi. We have a Rheem RPKA--48JAZ heat pump which we installed about 15 years ago. I runs perfectly in AC mode, and also in heating mode as long as the outside temp is below 60F. But once the outside temp rises to the 60F range, it will repeatedly trip the high pressure sensor.



Our HVAC contractor is stumped. We had a problem last summer with the coils freezing in cooling mode, but that was a pinhole leak in the accumulator, which has been replaced and the system recharged. He's added a bi-directional filter and inspected the metering devices on both the outside unit and in the air handler.



Others have told him about a checkvalve in the compressor unit that goes bad. Does this unit have a TXV in the compressor? Could that be the issue?

RJ_4

heat pump

Check your air side,   filter, dirty evap coil?  check duct size and take air flow readings. look for registers being shut off  check to see if AHU is the right size

Eugene_Silberstein

Very Likely an Indoor Airflow Problem

When an evaporator coil freezes, in this case the indoor coil of your heat pump, there are typically two ice patterns present. One is a partially frozen coil, where only the first few tubes freeze and the rest of the coil is warm. The other is when the entire coil freezes.



In the first case, there is either an underfeeding metering device or a refrigerant undercharge.



In the second case, which usually is accompanied by a frozen suction line, is almost always an airflow problem through the indoor coil.



Given that you had a frozen indoor coil in the summer, resulting in low operating temperatures and pressures, and high operating pressures in the heating months, it seems more than likely you have insufficient airflow through the indoor coil.



Be sure to check the filters, as mentioned, as well as the blower wheel itself to be sure it is clean and that the hub on the wheel is not loose. You can also check for closed supply registers or even, possibly, duct lining that might have come loose and is blocking the ductwork. In other words, you need to check all the components of the indoor air distribution system.



Please keep us posted.

PaulLambert

trips

When the coils froze up last summer, the lines did freeze as well. The tech found low pressure in the system, and eventually the leak which cause it. After repairing the leak and recharging the system, it ran the rest of the summer without any further freeze ups.



And this winter, the system has been running fine as well. The lines get nice and hot, and our home is heated adequately with minimal need for the auxiliary resistance heat to kick in.



The tech found the coils to be clean - I replace filters 4 times year. The blower is fine, and airflow is appropriate.

Eugene_Silberstein

Freezing Suction LIne

If the suction line (the line that is connecting the evaporator coil to the compressor) is/was freezing, it is highly unlikely (even next to impossible) that the frost is caused by an undercharge of refrigerant.



If a system is undercharged, there will be less liquid refrigerant entering the evaporator coil, causing it to boil off in the coil further away from the outlet of the coil. This will cause the refrigerant, now in the vapor state, to heat up. This makes the suction line warm and will not allow frost/ice to form.



The icing of the indoor coil in the cooling season and the high pressures in the indoor coil in the winter, once again, indicate a problem with the airflow through the structure.



If you would like to discuss, feel free to contact me at (917) 428-0044.



Cheers!

PaulLambert

cleaning

I hear what you're saying, but when the inside coils were freezing up, the problem stopped when the leak was fixed and the system was recharged, and it cooled just fine for the remainder of the summer.



Likewise, it heats just fine when the outdoor temp is below say 50F. When the temps were staying below 30F for weeks, the system ran almost continuously for days on end, and never tripped out. But as soon as the outside temp rises to around 50F, the high pressure trips begin.



If it's an airflow problem, why would it be sensitive to the outdoor ambient temp? The air flowing through the inside coils would be at the return (indoor) air temp, which I would expect to be relatively constant, regardless of the outdoor temp (other than the little bit of outdoor makeup air pulled into the return).



Also, the high pressure line coming into the air handler is quite hot, while the return line back to the outside unit is room temp. Doesn't that indicate that the coils in the air handler are able to release the heat? If the coils were dirty and not allowing airflow, wouldn't the return lines be hot as well? I don't know what a normal temp drop should be, but it's easily 30-40 degrees, and wouldn't surprise me if it's 50+.



I've observed a couple of these hi pressure events with the HVAC tech while gauges were attached. Everything looks normal, then there is a sudden rise in pressure to the trip point (around 300psi as I recall).



I get the basic physics of refrigeration - I went to engineering school, albeit for a computer science degree. And I used to manage the construction and operation of large data centers, where the HVAC is a critical system, some of the ones we put in were pretty exotic (e.g. capturing heat from the computer rooms to heat office buildings).



These events have the feel of a heart attack - like something something suddenly blocks the refrigerant flow. That's why the tech installed the filter, to see if there was some crap circulating in the system, and it's why I'm suspecting a malfunctioning component, like the reversing valve or a TVX, not an airflow problem.



I suspect the summer freezeup and the winter high pressure trips are unrelated. The high pressure trips have been going on for years, albeit much worse this year. That would be consistent with an intermittently failing or weak component reaching its last days. The freezeup in cooling mode happened only once, and went away with the leak repair and recharge.



I'm willing to try anything at this point. What's the best way for a homeowner to clean the inside coils? Can I just pour water through them, being careful to not damage the fins?

RJ_4

heat pump

Assumption in the HVACR buisness  is the kiss of death.  I would revisit the entire install, startup and any repairs to system. Can you provide the following (1) make/mod/sn.  refrig type .  (2) line sizes liquid, suction  (3) was the system charge weighed in after repairs, what are superheat and subcooling readings.  (4) sketch of duct work or pictures showing supply and return duct dimensions as well as branch ducts (5) What press. is high press cutout actually tripping at ( what is it set to trip at )  (6) does the system have any kind if zone damper system. As far as coil cleaning would need what type of unit you have. finally review the basic heat pump refrig. cycle ( press./temp )  Here to help when I can

PaulLambert

Rheem High Pressure Trips

I appreciate the reply, but like I said, this is a system which has run flawlessly in cooling mode for 15 years, and which, until this winter has only occasionally had a high press trip in heating mode. I'm convinced it's an acute component failure, or maybe crud getting stuck in some component, rather than a design problem.

Ironman

Convinced?...

I'm not. And I do believe that I have a little more experience than you (40+ years).



Paul as long as you're convinced that it's an "acute component failure or some crud", then no one here is gonna be able to give you any advice that you would receive.



One thing that you're obviously missing is that as the ambient temp rises, the outdoor unit absorbs more heat energy which must in turn be rejected by the indoor coil. If there is an air flow issue, charge issue, non-condensibles, mis-matched component,etc., then you'll see the exact symptoms that you're describing.



If you'll provide the info that RJ requested or contact Eugene, you'll get some direction that will help. Is not that the reason that you posted here to begin with?

Techman

Help us help you.

I agree w/ the others. If you are convinced its a major component then replace the equipment asap for a major price. If the cause of your problem turns out be a slight over charge of freon then what? Also, that check valve in the compressor that is causing you problem, that might be the" hi pressure internal relief safety valve", but its trip point is a lot higher than the trip point of the hi-press switch .

RJ_4

heat pump

You still have not posted the info requested on 2-22-13, one item that would be the easiest to report on is what is the cut-out setting of the high press switch, I have seen these trip prematurely due to wear and the cheap material they are now made of.

PaulLambert

Forgiveness

I don't mean to sound disrespectful. I do appreciate your responses. Here's some of the info you requested, let's see if it helps:



1) Rheem RPKA--48JAZ

2) liquid side lines are about finger sized - 1/2"? (not at home to measure); suction side ~ 1/4"?

3) No, the tech recharged the system using pressure gauges and a thermometer.

4) Don't have the drawings, but it's a 3000sqft two story with the air handler in the basement. Return enters the bottom, passes through "W" coils, blower, then electric aux furnace. Branch ducts are 8" round to the main floor, and oval ducts in the wall spaces to the second floor.

5) the one time I saw a high press trip with gauges on, it was at about 300psi. The system was running at a steady, normal pressure for many minutes, then suddenly - in a matter of seconds - rose to around 300psi and tripped.

6) no zone dampers. There's a short loop from the top of the air handler through a humidifier mounted on the cold air return on the other side. However, I currently have a towel stuffed in this loop duct to prevent air flow to the humidifier (until I can replace the solenoid valve)



Trust me guys - I'm not trying to claim I'm an expert, or minimizing the value of your experiece. But I too have lots of experience with computer room systems: power (generators, UPS, switch gear), HVAC, telecom and computer, and am a decent troubleshooter at a macro level. There have been times when my lack of detail knowledge has helped us stay out of the weeds when trying to figure things out.



That's all I'm observing here: the sudden rise in pressure just feels like a valve is closing off when it shouldn't, or a piece of crud is coming loose and blocking some narrow passage, either in a component or place where there's some build up.



The tech suspected crud which might have come off the inside of the accumulator as it rusted through (it was mounted at the factory in contact with the sheet metal of the outside unit, and corroded through at that contact point). This is why he installed the filter.



He inspected the inside coils, and said they were clean. He pulled the 'orfices' from both the inside and outside ends of the lines, blew nitrogen through the lines, and said everything seemed clean and clear. He's stumped, and so is his boss, the owner of the company and a 2nd generation HVAC guy.



The tech went off and did a little research, and said "some other guys said you can have problems with the check valve in this compressor." I don't know if there is such a check valve in my compressor, or if he was really talking about a TXV that's inside the compressor housing.



These high pressure trips have been going on for years, although it was once in a blue moon until last fall. Since the repair of the accumulator leak last summer, and the consequent recharge, the trips now happen within a few minutes of compressor start, provided the outside temp is around 60F. At colder temps, it will run continuously for days without trips.



I can't do the repair work myself - I have neither the practical knowledge nor the tools. I'm using an HVAC contractor who is just as stumped. I'm just trying to not be talked into changing out an expensive component like the compressor or the reversing valve when the problem might be something simple that we've all overlooked.



On the other hand, if 15 years is all I should expect from this unit, which is running in either heat or cooling mode every day for probably 45 weeks/year, then let's get it replaced and be done with it.



Again, thanks for any advice, and forgive my persistence in asking questions.

Techman

Hi press trip

Before the unit triped on hi press, you stated the press were NORMAL , well a normal press requirers a normal outdoor/indoor air temp  also. What was that normal press reading?

PaulLambert

pressure

Sorry, don't know what the pressure was that the tech called 'normal.' All I knew was that just before it tripped, he said, 'oh, the pressure is shooting up.' When it tripped, I asked him what the pressure was, and he said about 300psi.



I asked whether this was the appropriate pressure for a trip, thinking maybe the limit device was tripping at too low a pressure. He said he was thinking the same thing, but that 300psi was about right.

RJ_4

heat pump

Interesting  You have a bypass humidifier, this could be the problem if the supply duct to your humidifier is to close to the return air duct.  Take a return air temp. reading at the return next to the unit after the unit has ran for 5 minutes, if the temp. goes up to 80-90 deg. your short cycling air. If thats the case get some duct tape and seal the duct to the humid. must be air tight.  Also 300 psig head press. cut outs are typical on water cooled r-22 units, alot of time i see 325 psig, on air cooled r-22 units, but this depends on the manufact. The check valves i believe your talking about are in the condensing unit piping, if they were stuck head press would hit 300 psig in a matter of seconds. Your line sizes should be closer to 3/8 liquid and 3/4 suction for a 4 ton unit depending on line length. the compressor has pistons a motor,  valves and a internal relief valve   no txv.

PaulLambert

Pistons?

Interesting. When I bought this unit, I was told that it had a scrolling compressor.



The original heat pump was a Lennox unit with a piston compressor that failed about once/year. It was attributed to the fact that it had no oil/gas heater in the compressor. On the really cold days (e.g. subzero) I can heat with a combination of solar energy and a wood stove and the heat pump never has to run. Consequently, the compressor was often having to restart in the middle of night, after not having run for hours.



The hypothesis was that this was allowing liquid to enter or condense in the cylinder(s), hydrolocking the compressor and frying the motor. One advantage for the scroller was supposed to be that I wouldn't have to worry about hydrolocking any more.



I have the humidifier loop blocked off with a large towel stuffed up the duct, but there might be a small amount of air slipping by. Putting duct tape in is a cheap experiment, although I have to wait until the outside temp comes up.



I'll look for a check valve around the condenser coils. Thanks for the info.

RJ_4

heat pump

Sorry was not thinking about a scroll compressor   anyway still no txv   a txv is a refrigerant metering device   get some temp readings at the return air, you dont need to wait till its 60 to see if you have a air bypass problem   you can pick up a digital thermometer at Target int he kitchen dept.

Ironman

I've seen it before

The Rheem AHU's from that time period are notorious for having undersized blower motors. Rheem would put a 1/4 h.p. motor where a 1/3 h.p. was the norm, then fudge the blower performance data in order to achieve a certain s.e.e.r. rating. As the motor began to wear, it would loose power and the air flow would decrease with it.



Add to that the possibility that the tech may have slightly over-charged the unit (if he did it in the cooling mode) to get the back pressure up and you have the exact symptoms that you're describing.



Paul,

your own description of the events is contradicting your hypothesis: namely, that the tripping occurs when the ambient is 60* or above. If it were a blockage or debris of some sort it would be happening at random outdoor temps, not just above 60*. This goes to prove what I stated above: that at 60* and above the outdoor unit is absorbing more heat than the indoor unit can reject.



It is definitely not a bad compressor or reversing valve; that would not produce the symptoms that you have.



How did the tech charge the system? Did he weigh it in? What were the super heat and sub-cooling? What were the ambient and indoor temps? Also need the exact sizes and length of the line set. Did the tech remove the old filter/drier?



There is also a simple procedure to measure airflow: BTU's / (Delta T x 1.08) = cfm. BTU's can be determined by turning on only the electric heat and measuring the wattage (actual amps x volts) x 3.413 = Btu's. Then measure the temp rise and use the formula above. You should have 400 cfm per ton min. All that's needed is an amprobe and a duct thermometer. Keep it out from a direct line of sight from the heat elements or else you'll get a false reading from radiant heat rays from the elements.



Airflow is the first thing I'd check.

RJ_4

heat pump

Paul , just curious what you found out on your high press trip problem

PaulLambert

Optimistic

Thanks for checking back. We haven't had any warm days yet, although tomorrow might be. However, absorbing what you guys had said, I decided to take a garden hose, hook it up to a hot water tap, and thoroughly flush the coils in the air handler, using fairly low water pressure so as not to damage the fins.



The water I sucked up with the wet/dry vac was had a moderate amount of dirt in it, most of which I presume came from the coils. Since then, I've noticed that the compressor isn't running continuously on our 30F days as it had been, and the temp differential between the hot and cold lines seems greater - suggesting that there was problem transferring heat from the refrigerant to the air.



So I'm hopeful that the problem might be solved, and that it had to do with not being able to reject sufficient heat from the inside coils. Still don't understand the sudden pressure rises though...

PaulLambert

Thanks

And thanks for the advice... will report back if it trips out again...

PaulLambert

Good advice

Okay ... we've had a string of 60+ degree days, and no high pressure trips. So you guys were right - it was an issue with airflow over the internal coils. The cleaning with hot water and a low pressure hose seems to have done the trick - for free. I could have easily been talked into much more expensive solutions.



Thanks gentleman. Once again the smart-**** theorist was schooled by those who live in the read world!



PL

Techman

Mr.Paul

You Sir are a Gentlemen! Haveing a full responce from ANYONE IS EXTREAMLY RARE in this section of the wall . Thanks!

alotlikeearl

Another thing to check.

Paul,

Another thing you should check is the blower wheel on the air handler.  It doesn't take much dirt buildup in the vanes to really limit airflow.  Glad the problem has resolved.

                           Jerry

PaulLambert

fan wheel

Good thought, thanks. I gave it a good cleaning before the winter when I had to replace the fan motor, and damaged the wheel trying to get it off the shaft (which was about a foot long, so my gear puller wouldn't work). The new wheel went on with a liberal dose of Never-Seize.

PaulLambert

False indication

Victory declared prematurely. Hi press trips are back, temps in the 60s. Not sure where to go from here...

PaulLambert

Rheem High Pressure Trip

Well, here we are back to another heating season, and this problem has returned. I bought a couple of digital thermometers with remote bulbs, attaching one to each refrigerant line. Meanwhile, I've been trying to capture some data:



System off: Hot line (to air handler) = cold line = 70F when outdoor ambient is 64F



1) Outdoor=49F; hot line reaches 144F, cold line = 84F; normal operation

2) Outdoor=40F; hot=126F; cold=81F; normal operation

3) Outdoor=61F; hot reaches 153F; cold=84F; high pressure trip

4) Outdoor=61F; hot reaches 147F; cold=84F; high pressure trip



Outdoor unit is Rheem RPKA-48JAZ



Over the summer, I flushed the inside coils with hot water at low pressure. Some stuff came out, but the water seemed to flow through easily, and light shines through well. All the registers are open in the house.



The fan runs on high speed when it thinks the heat pump is operating, and it runs at low speed when I flip it to emergency heat. The emergency heat (resistance strips) seems to keep up okay, not having to run continuously with the outdoor temp at 60F.



I really don't want to replace this system, but I'm not at all confident that it's fixable. I always get the notices from the power company that our usage is higher than expected, especially in the summer, but I attribute that to the pool pump and all our southern expoure. Maybe it's the heat pump that's the problem.



Appreciate any advice.

Techman

Hi Press

Hi Paul. You seem to get along w/ your AC guy , so I would remove about 2 seconds  of liquid  from the LL and watch the press drop a little. Then recheck all of the readings.

Mike M

getting things clear

If your indoor coil freezes its from a lack of airflow across the coil....If this happens in the winter, you will get a high pressure trip.  The cause if it goes up all of a sudden is the indoor motor has stopped running hense a lack of airflow across the coil AGAIN.  A high pressure trip is 410PSI not 300PSI.We are assuming this is an R22 system.  If your hearing the internal bypass pop, which sounds like a louds swooshing sound, your mechanic didnt connect his gauges to the proper ports if he's reading 300PSI. He should be connected to the discharge line a few inches from the compressor, if he is, and the compressor BYPASS is popping, then the compressor is junk. That shouldn't happen til almost 500PSI.

      Thats a 4 ton unit I think, if it is, the line set is way too small in accordance with the sizes you gave us.  Also Dollars to donuts Its way over charged.  The indoor outlet temp in a heat cycle, should be around the 90-108F area.  Heat pumps dont blow hot air, they blow warm air. Typically indoor temp + 30F.  The crankcase heater is required (it has a reciever tank) unless they are using the start winding to heat the crankcase.

    There is also the possibility of non condenseables in the system.  When this pressure trip occures is it a pressure switch? (read the numbers on it using a mirror to see the back side) this should have the range.  Does it have a manual reset?  a red plunger button between the two wires connected to it?

   As far as a check valve, they DO have one on some ac units in the condenser coil not the compressor, it would be in the unfinned section with a steel ball bearing that can be heard using a magnet to slide it back and forth, it would also be near a small drier I believe if they have one. 

     Did the mechanic purge the system with nitrogen while he was brazing?  If not, as most don't, this could cause black oxidation flakes to jamb up internal things when it is charged. 

     In short, I think you are either overcharged or the indoor fan motor is cutting out for one reason or another...My money is its overcharged...simple fix, Remove a pound at a time and charge it to indoor ambient + 30F (no strip heaters involved) or better yet, use the RUUD/Rheem refrigerant charging scale. Its usually a decal on the door panel. Make sure the insulated line is a MIN of 1/2 wall, 1" prefered. Also heatpumps are not a primary sourse of heat where temps go below 30F. This is sometimes refered to as the balance point. Its efficiency is equal with electric baseboard strip heaters.

Mike

checked your lineset size should be 3/8 and 1-1/8" OD for 30' run or less, and 12#8oz of R22 for 25' Line set

don_9

Spike

We had these issue with lennox equipment on new installs years ago when lennox went to scroll compressor.We were told that the scroll would spike in pressure that the naked eye could not see on the gauges which was the reason for tripping.so we went back and turn them into automatic switches bc we wanted to be home for thanksgiving.lol

Most of the trip I see with them are due to being new heatpump on old airhandler and now you have a refrigerant imbalance which will have you making a visit to the house to adjust charge every season.

15 years old do you say?Replace it,it has passed it life expectancy