Coleman heat pump problem

JohnBob

I'm looking for any insight into why a  Coleman heat pump system (originally installed in 9/09) is only producing  11 degrees across the coil. The system consists of a THGD36s21 condenser, MC43b3xh1a coil and a MA12bn21 blower .The charge was weighed in to the amt required for the run. Since the install I have replaced the txv and coil under warranty.(under direction of Coleman Tech over the phone)  At 86 OAT the pressures are176/76 the suction gas temp at the evap and condenser are within a degree or two at 67, and the liquid temp is 88 at both. I let the system run and removed the evap cover to take temps of the individual lines coming out of the txv manifold, and 1 was just above 60 deg, 4 others were in the 70's and the last was near ambient of the attic (90). I know it sounds like the spider manifold is clogged, but I figured changing the evap would have eliminated that problem. Again ANY thoughts would be appreciated

Techman

Coleman

Can you verify that there is a full liquid line @the TXV ? If yes,what is the comp amp draw and what is it supposed to be? Possibly  a weak comp ? What type of comp is in this unit?

JohnBob

weak comp?

I had neglected to put in the original post the colman tech also had me change to compressor and Heat Pump valve (incase there was leakage through it)

Techman

Spider

plugged?I think the suction would be low in that case!Going back there anytime soon? @ 86* OAT the hi side should be around 250- 265 psi.

JohnBob

coleman

I was thinking at least the highest temp spider may be clogged, but don't know how I'd clear it.  Every other "normal" reason for low delta across the coil seems to be ok ( I changed fan speeds with little result). I was thinking maybe a clogged strainer before the txv, but then my discharge pressure would be higher and suction low. I'm going to take temps on an operating system and see how they compare

Eugene_Silberstein

Some Thoughts

With an outdoor ambient temperature of 86 degrees, you should be looking at a condenser saturation temperature of about 116 degrees, which corresponds to a high side pressure of about 243 psig. With a condenser outlet temperature of 88 degrees, you are operating with only 5 degrees of subcooling, based on your high side pressure of 176 psig (p3 degree saturation temperature).



From these two items (low condenser saturation temperature and low subcooling) the condenser is operating with a deficiency of refrigerant.



What was the temperature of the return air?



Your evaporator saturation temperature is 45 degrees (from the 76 psig) and your evaporator outlet temperature is 67 degrees.



Based on your numbers, your evaporator superheat is high at 22 degrees (67 degrees - 45 degrees). This also indicates a deficiency of refrigerant. If the room temperature (return air) was above 80 degrees, I am quite certain you have a refrigerant charge problem, since all indicators point in that direction.



A blocked or clogged distributor line would be consistent with the high superheat, but not the high evaporator saturation temperature. If the distributor line was blocked, your condenser subcooling would be high, not low.



If I was a gambling man, I would say the occupied space was warm to hot and that the system is undercharged.



Please keep us posted.

Eugene_Silberstein

A word about the reversing valve

One quick way to check a reversing valve for internal leaks is to take a temperature readings of the four ports on the valve.



The port that is returning suction gas to the compressor should be (pretty much) the same temperature as the port connected to the outlet of the evaporator coil. If the suction line port is significantly higher than the evaporator outlet port, you can assume that the reversing valve is leaking internally,

Techman

Deficincy of refrigerant

I like that!!!Some day if I grow up I want to talk more like you! Have a good summer,Professor!

JohnBob

coleman

The air leaving the evap was 71, air entering was 82

I'm going to be back there tomorrow or the next day, I'll try adding gas , but I'm pretty sure my calculations for weighing it in were accurate, although at this point I'm starting to doubt my own sanity.

Techman

At the AHU

you usually FEEL the activity in the liquid line.Hold the liquid line firmly,close your eyes and become one with  the freon .

JohnBob

problem persists

Well, I got back to the problem unit today, As suggested I added refrigerant till the amperage matched (approx) the values on a chart that coleman had faxed me last summer.

My super heat is still high and the temp across the evap is lower than before. Here's today's #s

Air ent evap  76

air leaving evap 71

Rh in the house was 45% or around 55deg wb

The unit is supplied w/ 243 volts, amps on the R teminal going to the comp 7.2 and on the Cterm 8.8 the coleman sheet says it should be 8 ( RLA on thedata plate is 14.6

Pressures were 185/63

suct temp was 55-57  liquid temp 73

I opened the coil section and all spiders going to the coil were approximately the same temp around 58 deg

fan speed is on high, but lowering it didn't change things much