Air Conditioning - Slow cooling A/C

I don't believe our a/c unit is working as good as it should. Right now we are having a heat wave (for Northern Ontario anyway, mid 80's) and our 2 year old unit cannot keep up. My wife usually turns on the a/c around 3pm when the thermostat is reading about 74 and by about 8pm it reads around 77. So in that 5 hours it usually loses 2 or 3 degrees (and thats with the upstairs and blinds buttoned up). Usually after 8pm (when the sun drops below the hill) we open the windows and let the breeze cool down the house. This seems to work a lot faster than with the a/c on. I'll tell some details of my situation.
The house is an 1100 sq. ft. bungalow with a basement (1100 mainfloor & 1100 basement). The front of the house (40' long) 3 windows including a large (10' x 5') bay window which recieves the late afternoon (direct) sun between 3 - 8pm (now in June).
The a/c unit was installed 2 years ago and it is a 2.5 (or 1.5) ton Armstrong unit with a SEER rating of 10. The furnace (and a/c) fan is run by a belt driven Emerson 1/2 - 1/6 hp, 1725 - 1140 rpm motor which seized up about 4 years ago. I oiled it up and put it back in service. I checked the current after that and it was drawing about 9 amps while pushingwarm furnace air. The area around the cooling coils in the furnace had to be unclogged last year by a professional.
I think the thermostat may be reading low. It reads 2 - 3 degrees lower compared to a mercury thermometer (thermostat read 74, thermometer reads 77).
The vents in the front room seem to be 15 degrees cooler than the thermostat reading temp. The return vent is located on the floor on the mainfloor (not near any output vents).
The first time we put on the a/c this year we still had the vents in the basement open and it got down to 59 degrees down there. We then closed all of the basement vents (as we do every year).
We (my wife) do not use the stove much.
If I told you anymore my wife may hurt me (lol).
The unit seems to be working good but we just can't seem to cool the mainfloor as quickly as we should be able to.
Is there too much heat coming in the bay window? Is my fan motor too weak? worn out? Will raising the return vent near the ceiling help?
What can I do?

Close the place up, set the thermostat to a temperature at which you are normally comfortabe, & leave things alone. Opening windows at night does more harm than good. It may take a couple of days to get the house humidity down to normal levels after which you should be comfortable.

We went camping last weekend and left the unit set for 71 degrees on Saturday. We left it that way until Tuesday and our situation did not change.
Another thing do ponder is this past winter I bought a top notch filter and the fan ran weird. Usually the furnace (fan) would kick in and run it's cycle and kick out. But with the good filter the fan would run for awhile and stop for about 5 min. back on for 1min. off for 20 seconds and than back on for about 10 seconds. I changed back to the old filter and it ran normally again. Would this be a sign of poor air flow due to the motor or blockage.
I said in the original post the coil area was cleaned last year and we have had motor troubles. Has anyone ever heard of a fan working in this manner? Is my motor powerful enough beacuse it was sized for the furnace and I know cold air is harder to push?
As you can see I am leaning towards a motor to possibly help (besides if I buy a new one this old one can be a spare). Does anyone know any details of the energy efficient motors?

Can you tell if the outdoor unit is even running?? Check the fat insulated copper line, it should be beer can cold if it's been running for a while.

I might add that a belt drive blower isn't the best choice for residential a/c. You could check the belt and make sure it's in good shape and tight as possible without being to noisy or over amping the motor.

Those new high efficient filters are very restrictive. Stick with th trusty $5 dollar pleated.

The unit is running well, I haven't checked the lines but it makes noise and I'm getting a 17 - 19 degree difference between the vents and the return vent.
I do have a $5 pleated filter, the belt is in good shape and the motor is mounted properly (level and in line with blower, no noise). All that seems fine as with the unit itself, I think I'm not getting enough air flow.
Tonight I did a complete check of the motor and it also seems in fine condition. It is spinning at 1740 rpm and with the use of a better digital clip-on ammeter the current was 4.8 amps. This is a big difference from the 9 amps I thought I read with an old ammeter a couple of years back (as stated in my original write up). I can hear the starting switch disconnect the starting winding.
Seeing as this 1/2 hp motor is rated for 8.7 amps and I'm drawing only 4.8, as well as having a 17 - 19 degree temp. difference. Do I have some room to move with my pulley sizes? I think I do? How much can I move?
My blower pulley would be the prefered one to change. So if I were to change that pulley from a 6" to a 5" that should give me a 20% increase in blower speed. Has anyone out there had any experience in changing pulleys? Will this make much difference in my flow? Is there any other factors I should be looking for? Oh yeah, I've closed my basement vents so I only have 7 vents open, will this be too restrictive?
Bob

Start with a good coil cleaning on the inside and outside, also clean the blower wheel really good.. The pulley on your motor may be adjustable. but be careful. If you start to get it to tight you'll get noise from it.

To Mattison's suggestions & comments I would like to add that by increasing the air flow, the temperature difference between the supply & return will decrease.

I didn't change any pulleys tonight (too busy with the kids after work), but I did some more checking. What I checked is the current draw with the a/c on and the current was 7.7 amps. I than checked it with the a/c off (turned fan on manually) and it was 4.7 amps just like last night. I have yet to take the blower off (tomorrows task) to look up inside but that seems like a big difference. I have read that cold air is harder to push but is it that much harder? Or once the a/c is on is there something else happening up in the plenum area? Anyone have any knowledge on this situation.
When I do change the pulley I will recheck the temperature difference once again. I will also clean the blower wheel and see what I can do with the coils.

Bob

Well, today I changed the motor pulley from a 3.25" to a 4" and what a difference it made. While I had everything out I also cleaned the coil with a dishwashing brush and very thoroughly cleaned the blower. For the blower I used the same brush as well as an old tooth brush and an air compressor. Another thing I did was I cut about a 10" x 6" hole in the return duct in the basemant (there is no return vent in the basement). I thought this would help in my attempt to increase the flow.
The outcome was very good, once I had everything back together the thermostat read 84 and within 3.5 hours it was down to 77. During those same hours, before the changes, it would be lucky to hold the temperature. I checked the temperature difference again and I still had a 16 degree difference, so not much change there. But there is an obvious increase in the flow out of the vents. About the biggest concern I had in trying this was the load on the motor. With the a/c off the motor was drawing 5.4amps and with the a/c on it was drawing 9.5amps. The nameplate FLA is 9.8amps (the website says 8.7amps) so I'm cutting it close, but it ran for 3.5 hours without cutting out.
I'll try setting the thermostat tomorrow and watch for a full day to see what happens.
If anyone has any input or other things I should be looking for please let me know.

Bob

If you like it go for it. But most coils work or call for a 18o to 20o drop over them . Also more air might feel good to you. But if you check at the higher CFM you dont take out as much humidity as you did at the slower speed. Some of the new AC units now . Start with a very low blower speed for a short time and then go to a higher speed that way they dehumidifi the air better.

ED ;)

Thats good to know Ed. Maybe I'll try the 3.5" pulley today and see how that goes. Ideally I would have liked to find a 3.75" pulley but I could not find one.
Come to think of it Ed it did feel a bit more humid in the house last night.

Bob