florida heat pump

[blewbyou2]

FHP model EMO048-3HZC serial DAO97215. Original call was continous blower fan, the cause was stat never would satisfy in heating mode. This is a water source heat pump. My loop temperature is 77 degrees F, clean strainer and 12 gpm flow. Charge was removed and weighed back in. Metering device is cap tube. 70 degree indoor temp, low load. Blower speed low. Cleaned evaporator and checked blower rotation. Cooling mode pressures 75/250, 0 superheat and 18 subcooling, 20 degree delta across evap. Heating mode pressures 36/175. Now here's the kicker 50 degrees superheat?? Reversing valve appears to be shifting properly. In heat mode refrigerant cap tubes frosting back to condenser loop? In order to bring heat on until I can resolve this problem I blocked about 2/3 of evaporator coil. Cap tubes are suspect but why the difference in superheat from heat to cool? Any help greatly appreciated.

[just_opinion]

more than likely your evaporator coil is full of oil in its lower tube. Thus, when you run in heat mode, the oil cannot pass through the cap tube with such low delta pressure.

Run the system in cool mode at highest blower speed (note that you have 0 degrees superheat in cool mode) and get some heat load on the system (flood light or something). Hoping that the oil gets back to the compressor, then run heat mode.

Good luck

[just_opinion]

The data you have there is not good either.

Water cool system with water temp @ 77 degrees and you have 250 PSIG. Also your evaporator pressure at 75 psig, which mean 42 degrees coil. With such low load and you have 20 degrees delta

[supertek65]

Hmmmmmmm low superheat high subcooling high head and high suction even for an average load. Is your amp draw too high? Discharge superheat high?
maybe you should check your SCALE!
LOL Frank

[r404a]

blewbyou

I think that the answer to your problem can be found with the answer to an important question. What is the temperature difference between the wate in and water out in both modes. You know you have the right charge. That is square one. Oil logging...very unlikely in a close coupled unit. Lets go back to basics and forget the exotic stuff for now. No knock on just opininion, but if you are scaled waterside and you can't get rid of heat in AC, you get a high head. I think your head is a little high. So, you have proven FLOW but how about transfer? A low temp rise in ac on the waterside with proven flow says scale. Now, in heat you look at a low back pressure. What I can't explain is high superheat and then 0 superheat. That being said, (A) verify measurements and (B) lets get temp splits on the waterside. Good luck.


r404a

[just_opinion]

If your water loop is scaled up, then you will not have high sub-cool. Don't you agree R404.

Also his post states that the cap tube is frosting right after the condenser in heat mode. This tell us there is something ristricting. I don't think there is drier (unless someone add a drier). Thus, there is oil in that condenser coil since it runs such low superheat in cool mode for long time and the oil is migrated in the coil.

It is just dicussion. So none taken there R404. We are only trying to educate ourselves.

[r404a]

just opinion,

you are right, high subcool probably wouldn't be seen on a scaled HX, but I have a hard time with flooding one way and starving the other way. Someting doesn't jive. That said, water splits HAVE to be taken on watersource so we get the full picture. Also, if he pulled the gas again, it wouldn't hurt to cut the air coil outlet and blow it ou. That would be to check for oil. I still think that would be a stretch, but, maybe if this thing had a few compressors in it, it is possible.


r404a

[jason_c]

just a stab, but did you change the drier? made sure to use a bi-flow? i just installed a drier backwards yesterday, but caught it before i added the gas good luck

[joeywpittman]

http://members.cox.net/epittman2/hvac-talk/FHP%20EM048.JPG

[emcoasthvacr]

On a cap tube, high superheats are normal if the evaporator is seeing high latent & sensible heat loads.

Another reason causing high superheat is that your suction pressure and temp is lower than normal, which starves the evaporator -- this cries out low charge.

[r404a]

The man said he pulled and weighed in the charge. This is a crucial step in proper operation and troubleshooting. I can't see how , if we have the same metering device being used in both modes, a cap tube, that we can have a restriction. I am really curious to learn what is found on this one.

r404a

[just_opinion]

emcoasthvacr,

The system is not low on charge because it has 0 degree superheat on cool mode

[joeywpittman]

?1 77* loop is that temp the supply or return

?2 how did you verify 12 gpm

?3 what is the chances of the original charge having air in it. was the original charge put back in



[Edited by joeywpittman on 11-06-2006 at 06:37 PM]

[emcoasthvacr]

Is there any chance of a leak? I read that the original charge was recovered, then charged back in with a scale.

Was the system properly leak tested prior to recharging?

Still trying to fiqure out that high superheat -- lol.

[heatingman]

sounds to me like you're having a ploblem with your reversing valve. If you properly weighed in the charge, we know thats not the problem. if you verified the 12 gpm, that's out. If the indoor temp is 70 and the loop temp is 77, that by all rights your suction pressure would be higher in heat mode than in cooling mode. In cooling mode the revesing valve is slightly resricting the refer flow to the water loop causing elevated subcooling and therefore acounting for the 20 degree gain accross the indoor coil w/o adding superheat, and the higher than normal dicharge pressure. In heat mode, the reversing valve is yet again reducing refer flow to the indoor coil and causing the high superheat b/c water has a higher specific heat than does r-22 as a gas. Check for temp drop across the reversing valve. over 3 degrees can the valve

[just_opinion]

Heatingman,

At what position is the reversing valve in to have 36/175 psig and 50 degrees super heat and the cap tubes are frosting at the outlet??

At what position is the reversing valve in to have 75/250 psig and 0 degree super heat and 18 subcool and 20 degrees delta temp across the evaporator coil??

[heatingman]

Just opinion - Could you please clarify your question? What do you mean by position? Heat and Cool position, or something more specific. The slide mechanism could be stuck somewhere in the middle for all I know.

[just_opinion]

Heatingman,

Your educated opinion is that "sound like to me you're having problem with your reversing valve".

Thus, I would like to know at what position the reversing valve is to have such data that the original post has.

[heatingman]

If my theory is correct, which it may not be than I believe that the reversing valve would be restricted in the not quiet all the way to the heating mode. from fully moving to either the heating or the cooling possition. So in other words the valve has movement, but not full range bank to bank. Maybe within a 1/8 of an inch from totally reching either side. But now that I think about it, the more likey problem is that the liquid line filter is restricted and badly. But I can't rule either one out from 800 miles away. Easiest way to find refrigerant side restrictions is pipe temperature measurements. Anything that is changing the pipe temp will change the pressure.