hvac help needed

I need some help with my hvac system. Instead of going into the details I'll just ask for what I am missing.

If you are able and willing can someone please provide the following data from your PROPERLY FUNCTIONING central air system. It needs to be in similar conditions to here. 85+ outside temps and high humidity (actually, today was 102 but that's another story).

After the system is running and blowing cold air, measure the air temp at the intake grill. Then measure the air temp at the vent that is closest to the unit.

Then, switch the fan to ON so it will continue running. Push the thermostat way up so the outside compressor will cut off. Now, start watching the air temps again.

Specifically, see how long it takes for the intake temp and output temp to equalize. And actually, the output temp should rise higher than the intake due to the fact that the air picks up heat from the ductwork, which is usually in the attic.

If anyone can do this it would help me a lot. It will give me a baseline to compare my system to.

When mine is running, I have output air that is about 15F colder than the intake. But what I really need to know is how long your system takes for these to be equal.

I've been measuring with an infrared thermometer. It's quick, easy, and pretty accurate.

I've been in HVAC for a while. Your 15 degree temp drop is okay, hard to tell without a wet bulb reading from a psychrometer. As for the time to equalize, it doesn't really matter unless you are worried about your coil freezing, which won't happen with a 15 degree temp drop. As for IR, they are not always accurate in this application as they are actually reading the register, not the air. The best way to take the reading is to use a thermocouple insert probe and measure the return drop and the supply just about the A-coil. Second best is to measure the temp at the filter grille or or wherever your filter is, and the closest register to the furnace that has decent velocity.

15F is a pretty good load on your system. The system may run for hours before it backs off. Temperature is also affected by humidity. 72F @ 60% humidity will not feel the same as 72F @ 30% humidity. Generally its better to leave the system running during a hot spell. The heat load inside the house builds up very rapidly. Just leave it on and choose the highest most comfortable temperature. This also depends on is your system is running at spec.

Valpo Hawkeye said:

I've been in HVAC for a while. Your 15 degree temp drop is okay, hard to tell without a wet bulb reading from a psychrometer. As for the time to equalize, it doesn't really matter unless you are worried about your coil freezing, which won't happen with a 15 degree temp drop. As for IR, they are not always accurate in this application as they are actually reading the register, not the air. The best way to take the reading is to use a thermocouple insert probe and measure the return drop and the supply just about the A-coil. Second best is to measure the temp at the filter grille or or wherever your filter is, and the closest register to the furnace that has decent velocity.

Click to expand...

Yeah. I am trying to figure out if my coil is freezing. I don't think it is fully freezing, it at all. But I think it might be partially.

After I cut the compressor off, I continue to get cool air for 20 minutes. The intake will be 78, and I get 73 out of the first vent.

I actually pulled the side off the air handler to get a look at the coil. The IR reading was 60 at the top of the A coil, and 45 and the base. Why does the base read SO much colder?

And I know IR isn't dead on, but it's close enough for my pusposes right now. It DOES read the vent temp and not the air, but I have checked it against the thermocouple probe on my fluke and it agrees within 1 degree. The nice thing is that it reads so quickly. The fluke takes minutes to get an accurate reading.

Basically I'm trying to troubleshoot a brand new system that I think might be installed incorrectly. The company has been out too many times to count. On this final visit they "said" they found the metering orifice installed backwards, which was causing my initial freeze-ups. It still runs a LOT, and has trouble cooling below 77F.

We are is MS. It's 102 outside. My attic is heavily vented and stays about 120F. Before my extra venting, it was 140F up there.

But, we were seeing the same behavior even when it was only 90-95 outside.

My power bills are nice and low, so I can't complain there.

Edit:

Like right now. It's 82 outside tonight with 75% humidity. Inside it's 78 and about 48%. The air will cycle on and off when set to 78, but runs nonstop when set to 76. It will not get below 78. And while I was away, I set it to 80 during the day. When arriving at home, it will drop from 80 and 52% to 78 and 49% within 15 minutes. If it will pull it down 2 degrees and 3% in 15 minutes why will it not drop it any lower?

Crazy...


Edit again:

Ok, check that. After an hour and a half it has finally pulled down to 76 and 46%. It seems to be working better with the filter out (for testing purposes only). The filter that WAS in there was a 10% dirty pleated one.

Do you guys think the pleated filter is dropping the airflow too much?

How much is running a lot. I just put in central air in my house a couple weekends ago and it seems like it runs a lot too, but then we had the highest temperatures ever. I've noticed that after the first couple days that it creates much less water after the humidity got down to normal inside the house, when we first started up sunday evening water just poured out.

absolutely nonstop

Mine ran non stop most of sunday night but then monday started going to a normal cycle. Did the manual for the outdoor piece come with a little baggie with some parts in it, mine came with that little orfice and it was a different size than the one that came in the inside coil so it has to be swapped out. I don't have any temp problems to help you out, but my house is 1300sq feet, built in 1959 and 1.5 story. My unit is a 2.5ton 13 seer for comparison.

I wouldn't worry too much about temp differences at various areas of the coil. Depending on if it's a TXV, piston, or capillary tube, the liquid refrigerant boils off at different areas. It's possible that the first point of expansion is at the bottom of the coil and the vapor warms as it reaches the suction port on the top of the coil.

It sounds to me like you're low on refrigerant. A good general rule of thumb is that your suction line, the larger one that's usually wrapped with insulation, should be sweating at the condenser. There are a few conditions where that isn't true, but 90% of the time it is true. Outdoor humidity is irrelevant to the operation of the unit. Outdoor ambient, indoor DB (dry bulb) and indoor WB (wet bulb) are the three factors, along with air flow, that matter most.

Without a gauge manifold on the condenser it's impossible for me to tell what your charge is like. Additionally, without an indoor WB and an outdoor ambient and the suciton line temperature I couldn't tell you if your charge is correct.

Eugene said:

Mine ran non stop most of sunday night but then monday started going to a normal cycle. Did the manual for the outdoor piece come with a little baggie with some parts in it, mine came with that little orfice and it was a different size than the one that came in the inside coil so it has to be swapped out. I don't have any temp problems to help you out, but my house is 1300sq feet, built in 1959 and 1.5 story. My unit is a 2.5ton 13 seer for comparison.

Click to expand...

How far off is the piston? If it's no more than .005", don't worry about it, unless it's really going to bother your, or it's under warranty. It takes a good hour to replace a piston since you have to pump the unit down, replace the piston, evacuate (vacuum) the system, release and re-charge, if needed.

turbodog said:

Ok, check that. After an hour and a half it has finally pulled down to 76 and 46%. It seems to be working better with the filter out (for testing purposes only). The filter that WAS in there was a 10% dirty pleated one.

Click to expand...

Okay, at 76 degrees and 46% humidity, you have a WB reading of 62 degrees. With those readings, the DB of the discharge air should be 56 degrees. If you have that, then your airflow is okay.

As for filters, the super-dense filters such as a purple Filtrete by 3M cuts airflow WAY too much. Use a cheap (approx $4) pleated filter, and that should be fine. The function of a 1x filter (meaning 1" thick) is not to filter the air of the home as much as it is to protect the blower motor and A-Coil from getting packed with crap and restricting airflow.

Valpo Hawkeye said:

How far off is the piston? If it's no more than .005", don't worry about it, unless it's really going to bother your, or it's under warranty. It takes a good hour to replace a piston since you have to pump the unit down, replace the piston, evacuate (vacuum) the system, release and re-charge, if needed.

Click to expand...

Is there any way possible to PROPERLY change the piston/orifice without pulling a vacuum? Maybe change it partially charged and let the refigerant blow out (thereby preventing air entry) during the swap?

Reason I ask is that when mine was swapped, they didn't pump it down.

By that time, the guy had made sooooo many trips out I am sure he was sick of hearing from me.

Valpo Hawkeye said:

Okay, at 76 degrees and 46% humidity, you have a WB reading of 62 degrees. With those readings, the DB of the discharge air should be 56 degrees. If you have that, then your airflow is okay.

As for filters, the super-dense filters such as a purple Filtrete by 3M cuts airflow WAY too much. Use a cheap (approx $4) pleated filter, and that should be fine. The function of a 1x filter (meaning 1" thick) is not to filter the air of the home as much as it is to protect the blower motor and A-Coil from getting packed with crap and restricting airflow.

Click to expand...

Well, I am pretty close then. When it does get down to 76, the output at the cloest vent is about 58-59. And I have determined that I usually pick up about 2 degrees from the duct, which puts the coil output temp at 56-57.

Valpo Hawkeye said:

I wouldn't worry too much about temp differences at various areas of the coil. Depending on if it's a TXV, piston, or capillary tube, the liquid refrigerant boils off at different areas. It's possible that the first point of expansion is at the bottom of the coil and the vapor warms as it reaches the suction port on the top of the coil.

It sounds to me like you're low on refrigerant. A good general rule of thumb is that your suction line, the larger one that's usually wrapped with insulation, should be sweating at the condenser. There are a few conditions where that isn't true, but 90% of the time it is true. Outdoor humidity is irrelevant to the operation of the unit. Outdoor ambient, indoor DB (dry bulb) and indoor WB (wet bulb) are the three factors, along with air flow, that matter most.

Without a gauge manifold on the condenser it's impossible for me to tell what your charge is like. Additionally, without an indoor WB and an outdoor ambient and the suciton line temperature I couldn't tell you if your charge is correct.

Click to expand...

Good to know about the coil deltas.

The suction (low pressure side) is sweating, but not much. It's a Looooooong way away from the evaporator. I figure it's about 65' total.

I mentioned outdoor humidity because I know that the water vapor can literally travel right through the walls. Then the unit spends all its time removing moisture (latent heat) instead of cooling.


Also, one extra thing to complicate matters is that the digital thermostat must have a float/swing value of less than a degree. The thermometer never changes temp unless you are cooking. The rest of the time it stays DEAD on the setpoint. I read the manual for it, but you can't adjust the float/swing value.

turbodog said:

Is there any way possible to PROPERLY change the piston/orifice without pulling a vacuum? Maybe change it partially charged and let the refigerant blow out (thereby preventing air entry) during the swap?

Click to expand...

No, there is no way to properly change a metering device without a pump down followed by a deep vacuum. Two reasons: First, the contractor is releasing more than the "de minimus" of refrigerant that we're allowed to release, basically enough to purge our manifolds. Therefore, it's an EPA/ARI violation. Second, if there's still pressure in the system it's difficult to keep the piston seal, basically a teflon o-ring, and the piston in the housing. I've opened systems that have a nitrogen purge in them, for pressure testing, and there was still a little pressure in the system. It actually shot the piston accross the basement.

It is possible if you have a careless, incompetant contractor that you have non-condensibles (moisture) in your system. This causes excessive flutter in the pressures and reduces the overall capacity of the system. There's really no way to know without a gauge manifold on the system.

turbodog said:

Also, one extra thing to complicate matters is that the digital thermostat must have a float/swing value of less than a degree. The thermometer never changes temp unless you are cooking. The rest of the time it stays DEAD on the setpoint. I read the manual for it, but you can't adjust the float/swing value.

Click to expand...

I wouldn't worry excessively about this. I personally prefer a one-degree swing, but I know some honeywell's and others do a 0.5-degree swing. They claim it maintains a higher level of comfort. Of course, as you know, it also cycles the system a bit more.

Thanks. Will have a conversation with the contractor. They still need to come back out and connect the extra drains for the condensing furnace.

turbodog said:

Thanks. Will have a conversation with the contractor. They still need to come back out and connect the extra drains for the condensing furnace.

Click to expand...

What brand of equipment?

Goodman 4 ton coil and compressor with 95% nat gas furnace. This is cooling a 2300 sq ft new house.

Valpo Hawkeye said:

How far off is the piston? If it's no more than .005", don't worry about it, unless it's really going to bother your, or it's under warranty. It takes a good hour to replace a piston since you have to pump the unit down, replace the piston, evacuate (vacuum) the system, release and re-charge, if needed.

Click to expand...

I think the coil came with a .072 and the compressor a .065. we swapped it before soldering the pipes.