Restriction?

[Inches of Mercury]

ICP Commercial
CAC060HAA condensing unit with some ancient General Electric Air Handler.
R-22

low side - 35 psig
hi side - 210 psig
suction line - 32 deg
liquid line - 77 deg
supply air - 46 deg
return air - 69 deg
outdoor ambient - 81 deg

There was a "freezestat" that initially needed to be reset. Was set at 35 deg. The maintenance staff recently installed a new blower motor. I don't know if it was pushing enough air or not. I don't have an anemometer!:( I checked air filter, evaporator and the blower (made sure it was rotating the right way!) and didn't see any restrictions. I measured across the liquid line filter-drier and got 78.5 deg.

Originally I thought it was low on charge. I added refrigerant and the pressure dropped. Low side at 30 psig and compressor is getting louder. Couple minutes go by and the compressor makes a grinding sound. Shuts off, Contactor coil energizes, comes back on for <5 seconds and repeats 2 more times before I shut the thing down.

When I add refrigerant, the high side should go up not down! With the compressor making noises and shutting off did I overcharge it? Maybe some kind of restriction in the system?
:confused:

[cw0682]

High Subcooling, High superheat, Low Evap pressure, I think I would start by looking at the metering device and figure out why there isn't more liquid being let in the Evaporator.

[BigJon3475]

Can you use your hand on the sensing bulb if it's a TEV and flood the evap?

[kelvin-459]

Is it a TXV or piston? Possible the sensing bulb could have been knocked loose? Or just bad TXV?
Good luck

[Inches of Mercury]

No TXV. It has a Piston.

[miller-cold-filtered]

i would recover first because you already know that you over charge the systm.

second, i would check the blower motor. make sure its compareable with the old one. look at the horse power and rpm, etc.

last, check for restriction. could be the txv, could be a drier if it has one, could be mantenance guy bend liquid line partially.

good luck

[The Penguin]

low air flow check motor amps - compare with the unit name plate not the motor name plate - confirm the motor is pulling the max amps

if they replaced the "1hp OEM " motor with a 1hp jobber motor they will be low on air as the jobber motor will have a lower amp rating even with the same hp rating - you often have to go up in hp using jobber motors eg 3/4 hp OEM = 1hp jobber motor.

restriction you measured 78° across the dryer that is you had a 78° temp drop across the dryer? if so replace the dryer and you should be all set

[heatingman]

ICP Commercial
CAC060HAA condensing unit with some ancient General Electric Air Handler.
R-22

low side - 35 psig
hi side - 210 psig
suction line - 32 deg
liquid line - 77 deg
supply air - 46 deg
return air - 69 deg
outdoor ambient - 81 deg

There was a "freezestat" that initially needed to be reset. Was set at 35 deg. The maintenance staff recently installed a new blower motor. I don't know if it was pushing enough air or not. I don't have an anemometer!:( I checked air filter, evaporator and the blower (made sure it was rotating the right way!) and didn't see any restrictions. I measured across the liquid line filter-drier and got 78.5 deg.
:confused:

Is that 78 degree dirence one side to the other on the LL Drier? If so that is the problem. If not, Is this a pumpdown system?

[heatingman]

Could you Physically see the evaporator on both sides? You could be fighting a Iced over coil, and if you charge is this state, you might drop the suction pressure, as you add referigerant.

[51fitter]

No TXV. It has a Piston.

This question has been popping up on me lately. I conclude that I don't like pistons for expansion.

Now an explination. I replace a condenser. install it and find my suction low. Add gas and start to get liquid back to the compressor.

Install a new heatpump with an old AHU in place. In heating mode I get high head. In AC I get boarderline suction.

Old evap coils with poor heat exchange are the cause. And with a piston there is no fix or adjustment.

Poor heat exchange can becaused by a number of things.

I find dirty coils when the evap is thick. These are not on the surface of the coil and are very hard to clean. (compressed air/nitrogen/powerwasher).

old pulleys-reduced airflow over time. Check the motor amps and measure the cfms at the diffusers.

Coroded fins-A 15 year old coil might have all its fins but they sure don't transfer heat like they did when they were new.

Adding gas is not the way to go IF this is your problem. Compressor damage will be the result. Good luck because I don't have the answer other then change out the indoor AHU.

This is a condensed answer and explination.

[mikelcs]

at 46 supply and 69 return, i would start with airflow. check the evap. coil and blower amps. the grinding compressor may be flooding.

[wisecracker]

Is the blower running backwards?

[Inches of Mercury]

First to answer some of the questions -

1.5 degree difference across filter-drier.

I was wondering about the blower too - it's running in the right direction (due to the setup I couldn't see it while spinning, but blades are pointing in the right direction and when I held a piece of paper to return grill it stuck. Supply registers blowing out).

Evaporator was not iced up.

The Air-Handling Unit is OVER 30 years old. There is no info other than General Electric. So I'm not sure what size motor is supposed to be there.



So today I go back and boss has me recover, replace filter-drier and charge to manufacturer specs, thinking there must be some kind of restriction in the system (I couldn't find any restrictions in the duct work [filter clean, registers open etc...])


LOW - 30 psi 26 deg = 19 S.H.
HIGH - 135 psi 71 deg = 5 S.C.
69 deg return air
41 deg supply air
ambient 66 deg

I would think that even with the low ambient my pressures would be a little higher! Also with the high S.H. and low S.C. it sounds like a low charge, but I weighed in per man. specs.

After talking with the maintenance guy he said the Freezestat "occasionally" has to be reset. He didn't clarify if that meant once a year or once a month.

After it was fully charged, it ran for maybe 15 minutes before again tripping on freezestat. :(

I'm not convinced there is enough air coming out of the registers. My fault I don't have the proper equipment (no anemometer).

If you've read my rant on rookie mistakes you'll understand that I am VERY frustrated here. This was my 2nd time at this job and it still isn't fixed. This really bothers me and if it turns out I missed something simple I am going to SCREAM!!!

[wisecracker]

135 psig head pressure. Sounds like you need some fan speed/ cycling control to get that head pressure up. Try doing it manually first to see if your pressures come up. Just an idea.

[51fitter]

At 135 head and low suction that isn't charged fully yet. Unless it was 45 degrees outside. If it were 80 outside you should be running in the area of 228 head. (thats using ballpark numbers) but they come out very close most of the time.

[51fitter]

Forget about superheat and subcooling until you get closer to a full charge :)

[The Penguin]

Ok slick

1 how much juice did you put in
2 what was the indoor fan motor amps?
3 what was the rated fla on the indoor fan motor
4 what was the OEM motor amps - (indoor AHU name plate rating)


Now I'm reaching a bit here and I've been slammed before for saying this
but I'm going to say it again

your approxmate charge will be around 9 to 12 lbs r22 ( allot will depend upon the length of the lineset - this should get you into the range You should be able to find out the unit charge from the label and then cal the extra for the lineset - should get you close

I just did a york unit on an old ge ahu (7.5 ton) and my suction was 55 with a head of 180 and an ambiant temp of 72° 14 lb charge


so slick - I think you charge might be a bit low but I also think your air flow is too low - check and correct the air flow first assuming your ref charge is around 9 lbs or a bit more

[7th son]

Sounds like you have two problems. Think about it..liquid temp lower than ambient? That indicates a restriction in the high side ahead of the measurement point. Is the liquid line valve open? Restricted coil tubing? Where is the temp change in the condenser coil?
With the temp drop across the coil, the condenser and expansion device are doing some work. Probably have low airflow. Crank up the sheave to max out the motor amps.

[mikelcs]

[QUOTE=Inches of Mercury;1515458]ICP Commercial
CAC060HAA condensing unit with some ancient General Electric Air Handler.
R-22

supply air - 46 deg
return air - 69 deg
outdoor ambient - 81 deg

There was a "freezestat" that initially needed to be reset. Was set at 35 deg. The maintenance staff recently installed a new blower motor.
Low side at 30 psig and compressor is getting louder. Couple minutes go by and the compressor makes a grinding sound.

you are not moving enough air. check your new blower motor & fan

[heatingman]

Measure your superheat on the discharge line and compare it to the suction superheat. It sounds like your compressor is not perfoming very well, not oumping enough. The discharge superheat should be at least triple what your suction superheat is. You could have a busted connecting rod or something.

Both the superheat and subcooling levels sound normal for a piston system, which leads me to believe there is mechanical failure of some kind. If the blower were wrong, that would effect the suction, and the superheat would be in the tank, like 0. It sounds like there is not enough volume of refrigerant flowing. I would look to the compressor, not a valve issue, so much as a pumping capacity issue.