Air Conditioning - Insufficient Cooling

Hello guys, I am new to this forum and hope to get some help. I am out of ideas on this a/c problem.
I have a rental house of almost 1,000 square feet with a 2.5 ton a/c system. The tenant complaints often about not enough cooling, this is been going on for about two months now. I am south Texas and the weather here is in the 90's and 100's most days. Some of the things I have done recently to this a/c system include: Replacement of both the inside and outside fans, the blower wheel in the furnace, replaced the freon completely, the contactor, compressor capacitor, fan capacitors, cleaned the evaporator coil, and replaced the ac filter of course. There are no leaks in the system, the pressure on the low side is about 72, and the high side about 150. There are no restrictions as far I noted. I have gotten in the attic to check the ducts for leaks or damage and found none, I also noted that the house insulation is adequate, a little old, but ok. I installed two additional air vents to help with the air flow in the attic. The thermostat is set at 77 and the room temperatue only gets down to 79 in the mornings, when you raise the temperature in the thermostat above 79, the system shuts off ok. The weather outside is usually 92 or higher in the morning when we have those readings. Late afternoon, when the weather is 100 degrees or higher, the digital thermostat is kept at 77, and the room temperature reads 85 degrees. The tenant complaints that this is not cool enough for her and that the ac nevers shuts off. I have found nothing wrong with the system and have done all the above in an attempt to keep her happy and see if things improved. I tell her that the weather is too hot outside and that is almost impossible to for the system to shut off. She complains that even at night, it never stops. She now wants me to install window air units in every room to help the central air and I found that ridicoulous. There may be something wrong with the system, but right now is working every day and according to the tenant, non-stop. I do not want to replace the whole system, I know a bigger one will help. Is there really a problem here, or do I just have a nagging tenant? Is there a way I can improve air flow in the system? That is the one thing I have not tried. Even though I replaced the furnace fan with a new one, the air flow inside does not feel strong enough. Any ideas will be greatly appreciated. (I failed to mention, the evaporator coil is clean)

Joe

If your high side is only 150 psi, you got a problem. Are you sure about that number?

Yes, I believe so, maybe slightly higher, but 150 psi in the high side is correct.

Is the suction line cold? The low side pressure seems about normal but that high side is way too low. Temperature and pressure readings of the liquid and suction line would be most valuable here.

Offhand, I would speculate that you have a worn out compressor. 150 psi is more like a static pressure. Further testing is needed for sure.

You may be right, the compressor does have a kickstart. However I thought that if the compressor is working, that was all that was needed. Somebody told me to do a good vacuum and recharge the system again. I may do that, or just replace the compressor. Thank you for your reply.

Is the suction line cold? The low side pressure seems about normal but that high side is way too low. Temperature and pressure readings of the liquid and suction line would be most valuable here.

Offhand, I would speculate that you have a worn out compressor. 150 psi is more like a static pressure. Further testing is needed for sure.

I did replace the compressor with a new one yesterday, the high side pressure is now 210 and the low side is 72. Temperature outside is about 94 degrees. Would you say this are good readings? I suspect an evaporator coil restriction, but not sure at this point. If I was to have a restriction, what would be the easiest way to find out?

Joe

You need to check the panel on the unit. There should be a chart and it will tell you the proper charging procedure. You need to go by sub-cooling/ superheat.

I am not an expert and the subcooling/super heat method is unkown to me. Can you please tell me how exactly do you do something like that?

Joe

I have to ask. Are you EPA certified to do this work ?

Yes I am, universal. However, I do not do this for a living.

Evaporator Inlet Air Temperature Fahrenheit Wet Bulb

54 56 58 60 62 64 66 68 70 72 74
Outside Air
Temperature DB
60 13 17 18 20 24 26 28 30 33 36 39
65 11 13 15 17 18 22 25 28 30 33 36
70 8 11 12 14 16 18 22 25 28 30 33
75 5 7 10 12 14 16 18 23 26 28 30
80 4 6 8 12 14 16 18 23 27 28
85 4 6 8 12 14 17 20 25 27
90 4 6 9 12 15 18 22 25
95 4 7 11 13 16 20 23
100 5 8 11 14 18 20
105 4 6 8 12 15 19
110 5 7 11 14 18
115 5 8 13 16

From the chart above, what are the numbers on the top horizontal line?
How do you take a temperature reading vs pressure? Is it in the guage?
I have a laser temperature gun, would that work?

Let me add something,

Yesterday afternoon about 6:00 pm, I get a call from the tenant. She says the ac is not cooling ok, that the temperature inside was 89 and the thermostat was set at 77'. I went and found everything ok, the filter had not been replaced and told her to replace it since I did not have one on hand. The temperature at the air vent was 68' and at the return air grill was 83'. The temperature outside was about 95'. The ac system had been running about 2.5 hrs by then, but it felt very hot outside. I told her that we needed to wait until the next day to see if indeed there is a problem with the system. The pressures outside was 74' at the low side, and 210' on the high side. Would you say this ac system is working ok based on the above? Or should I keep trying to improve it? My tenant keeps complaining.

I am ready to try the superheat method even though I am not familiar with it. I am not sure I have a restriction in the coil. I am thinking I should replace the fan relay in the furnace even though the fan seems to be blowing ok. Maybe the high speed is not working. If I can stick a bigger and new uncased coil in there, I may have to try that. It has a slanted evaporator coil, can I replace it with an "A" coil? I am just feeling a little frustraded.

We need suction line temperatures and liquid line temperature to tell the whole story. Go get two digital thermometers and get those temps at the condensing unit. Make sure the probe has good contact with the copper line and cover with a small piece of insulation. Post back with the temps and pressures. Let the system run for at least 10 to 15 minutes before writing down those numbers. Also, wet bulb and dry bulb temps at the return air vent would also help.

Like Jim said more info is needed. The laser wont be accurate enough.

You stated that it had been running 2.5 hours when you were checking it. Are they shutting this thing down at night or something ?

A properly sized system can take a long time to get to setpoint after being off overnight and with the heat your seeing they should not be shutting it down at all.

She says the ac is not cooling ok, that the temperature inside was 89 and the thermostat was set at 77'. I went and found everything ok, the filter had not been replaced and told her to replace it since I did not have one on hand. The temperature at the air vent was 68' and at the return air grill was 83'. The temperature outside was about 95'.
The ac system had been running about 2.5 hrs by then, but it felt very hot outside.
First whats the temp drop over the coil at the coil???? ALso you cant turn a AC on and off when you want. Most of the time we tell people that it takes about 4 to 5 days before you can start to feel the AC and you feel cool . It has to get the humidity out of the home.

I'll stay out of the technical end of this, but thought I'd help by asking more about the house. Such as is this one story? What color is it? What color are the shingles? Lots of windows? Super hot attic without any special attic ventilation to speak of? Is the attic insulated, and with what/how deep? Is the condensor unit out in the hot sun?

(Short story on-topic, may be of assistance to poster)
I ran into this tenant the other day who is sort of clever. He smiled and told me about his jury-rig attic fan. I said, "What?" He explained that he took off the attic acess cover in his garage on a hot 90's day and the sun was out, and he set up a big fan in his garage to blow out the air, and he claims this created negative pressure in his attic and he could feel hot air being drawn out of the attic. And by reducing the super hot (140 degree?) heat in the attic, he claims this is helping the a/c cool the house.