need a ac doctor………………….
alwaysoverbudget
| Posted in Energy, Heating & Insulation on
i have a central air unit giving me trouble, blow a little cool air ,but not enough to cool the house in 100 degree heat.
heres what i’ve checked,
all the fans are running as they should.
air filter clean,
condensor is clean,
a coil not frozen and is clean
so i hook the gauges,it’s 85 degrees , low pressure is 75,high is only 175.[shoudn’t it be in the 250ish range]
the high pressure line coming out of compressor is so hot it will boil water off it,also does a pretty good job of burning the skin off 3 fingers also. :]
i’m thinking the high side is way low,and the compressor is shot,aka time to replace unit. any ideas?????????????
the older i get ,
the more people tick me off
Replies
You got a straight AC? No heat pump? Leaking bypass/reversing valve??
Sounds odd indeed... ..still thinking about it.
straight air,no heat pump.
that high pressure line is hot coming off compressor and it seems like the compressor is a little hotter than normal,
one of my first checks on a air is to feel the air coming off the condensor fan. when you hold your hand over the fan the air doesn't have much heat to it.so it's not pulling a lot of heat out of the house. when i left the house temp was around 84.the older i get ,
the more people tick me off
Burn finger hot is normal coming directly off compressor. I thought you were talking discharge from condensor.
Low liquid line usually indicates no heat transfer in evaperator.... froze up... no fan...air blockage etc.
Do you have an internal dryer filter? Any temp. differance on each side of dryer? Possible blockage?
If blockage/restriction was outside unit then it would lead to higher pressure.
Compressor is suspect but I wouldn't condemn it just yet.
I would 2X check first for dirty evaperator/icing/restriction.
Ice could have formed and you didn't see it..... run fan by itself for 30min to confirm no icing.
does have a filter just inside the unit on the high side.i did touch it,can't say for sure but it didn't catch my attention with differences in temp.
if a evaparator is not flowing air correctly,does the high pressure go up or down?
i think if a condensor is restricted your high side goes up?the older i get ,
the more people tick me off
if a evaparator is not flowing air correctly,does the high pressure go up or down?
Pressure will go down on hi side.
Your quick walk by test of feeling for warm air coming off the condenser confirms no heat xfer from evaporator to condenser.
No heat xfer on your condenser and hi side will rise.... but that is not your current problem.
Since you can't visually confirm no icing... I would run fan for at least 30 min with unit off just to make sure.
went there this am,just couldn't find a problem, so i put in a new unit.seems ok but a few days of this 107 degrees will wring out if there are other problems.
got into something i hadn't done before. i put in a heat pump unit,but only using it for the air. made for a little confusion on wiring,but when i left it was blowing cold inside and hot outside,so i hurried up and left.the older i get ,
the more people tick me off
Low airflow would be my first stab.
Then improper charge.
are you thinking low airflow over the a coil also? i didn't take the front housing off,just undid a corner and peaked in.
i was looking for iceing,but to tell you the truth,it's a upflow so i'm not seeing the underside of where it would be dirty.the older i get ,
the more people tick me off
Well, it is just a guess.... without knowing anything other than gauge readings.
If it worked last year, and doesn't now, I would lean more towards a leak resulting in a low charge... after making sure the filter was clean... and the condenser was clean. Of course, the low charge could lead to a frozen evap.
The only way to tell if an evap coil is dirty without actually looking at it is to take static pressure readings.
I don't understand the refrigerant side like some of the other guys. My take would be to check the discharge air temp off the coil ... or from the register into the room. If it is really cold (e.g. 45 degrees), then your cooling fan speed isn't kicking into high.
I learned this troubleshooting for a client once who couldn't figure out why her house wouldn't cool down even though it felt like cold air dumping into the room. The reason is there isn't enough air flow to 'get it on'. This may affect some of the symptoms in the A/C side, too since you cannot transfer enough air across the evap coil to get it warmer .... that's where my knowledge falls off quickly.
Cooling on residential sized units require a high speed air flow across the evap coil. You should supply e.g. 55 degF air to the rooms, not 45. Low temp means there isn't enough air flow across the coil ... air comes out of the register at low speed and either floats across the floor .... or dumps straight down from the ceiling w/out mixing in the room. This is about air volume flow ... you need more in cooling to do the job. It's common that the motor speed gets set wrong for whatever reason. I've seen it many times.
That's my 2 cents.
The biggest problem is any type of 1" pleated filter- those restrict too much airflow. The thicker ones max out at 1600 cfm **when the filter is clean**. Claims of supporting 2000 cfm are greatly exaggerated.
Airflow/filter problems are magnified when the ductwork at the equipment is crappy. Static pressure reveals the flaws.
Setting fan speed without checking static pressure is pointless. It is possible to get *more* airflow on a lower fan speed.
If you check the superheat, you will know if the airflow is good.
ok,you said the magic word. super heat. can you explain that to me and how do i check it?
i swear all i see hvac guys do is throw gauges on and bring the pressures up to lets say 75/ 250 and go home.
how do you treat a sight glass,clear means it's all good or do you go ahead and pay attention to the superheat???the older i get ,
the more people tick me off
Superheat is the temperature of the refrigerant *above* temperature shown on a pressure/temperature chart.
Subcooling is the opposite.
Example: R22 at 68.5 PSIG should be at 40* F
If you measure 50* F, then you have 10* of superheat.
To check it, you must have a set of accurate gauges, a pressure/temperature chart and a digital thermometer that will clamp/wrap around the lineset.
To check the charge, you must have a charging chart (sometimes in the unit) and a psychrometer to get wetbulb temp readings... plus the above.
Outdoor coil and air filter should be clean first.
The guys that shoot for 75/250 are doing it wrong... but it takes time to do it right, and there is no way it can be done right during the $69.95 "clean and check".
Do not charge to "clear the glass". It will be wrong.
In order to charge an AC unit, you need the following at a minimum:
Airflow
Clean filter
Clean condenser
Hi and Lo pressures
Hi and Lo actual temperatures
Temp/pressure chart
Indoor wet bulb
Outdoor dry bulb
Static pressure readings will tell you if the indoor coil is plugged/restricted.