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rjordan392 08-07-2007 03:15 PM

Temperature Differance Over Coil
Is it time for me to call the HVAC serviceman? The incoming temperature and outgoing temperature is 14 degrees differance before and after the A-coil.

Things that I checked:
Indoor temperature was 76 degrees.
Indoor relative humidity as noted on the Bryant evolution control was 60%.
Outdoor temperature was 95 degrees.
We are going through a hot spell with high outdoor humidity. There is also a pump installed to direct the coil water to a drain and I have not heard it kick on at all for at least a week.
I also took the cover off where the coil is located to check for water at the base and it was dry.
The coils were not frozen over.

This is a new complete system of a Bryant two speed puron plus model 598B condensor and a new furnace, the Plus 80V with an Evolution thermostat that was installed two years ago. Did I lose some puron or is it a malfunction?

bigMikeB 08-07-2007 06:06 PM

Sound slike the charge is low, leaks in the system should be warranted for two years.

rjordan392 08-07-2007 08:10 PM

My HVAC man inspected the cooling system back in April of 2006 and all was ok. I will give him a call. Am I within my rights to demand he fix the leak before adding more refrigerant? On most occasions, a mechanic is sent out without a leak detector and just a set of guages and a tank of refrigerant.
I don't want to have to pay for this type of service every two years, it don't seem right.
And if the system has a leak, does that mean contaminates got into the system and then requiring evacuating the system to draw it out before charging the system to capacity?

Of course I will have to wait for the diagnosis as it may be something easy to fix.

bigMikeB 08-08-2007 06:09 PM

HVAC service techs have a legal responcibility to repair a freon leak, they can be fined by the EPA for dumping gas in a unit knowing it has a leak. You have them by the short hairs if that's what they have been doing.

rjordan392 08-08-2007 08:08 PM

That's good to know. The system uses Puron; is that still Freon with a differant chemical makeup? But Lets not judge too soon, I will allow the technician (hopefully he is) to check out the system and see if the problem is in the curcuit board. If its a leak, then I will insist he find it and repair it and perform the services required upon fixing a leak.
I saved a copy of your instructions for this that you gave to Yummy Mummy. I did inquire last season that I felt that the condensor fan speed did not appear to be in high speed because I still recall how my old system kicked into high speed as I was outside when it happened. Two seasons have passed and many a time I was out back working near the condensor and have never heard it go into high speed. The whole NE coast is under a heat wave with temperatures approaching 100 degrees with high humidity and the only relief I get now is with the help of a dehumidifyer in my basement and a window airconditioner in an upstairs bedroom to supplement the AC.

rjordan392 08-09-2007 10:23 AM


Yesterday my system was not pulling out any moisture that was measurable as my thermostat indicated 60% rh all day and the outside temperature reached 96 degrees. The system was cooling and I could keep the temperature maintained at 77 degrees, but why there was no moisture removal has me perplexed. Now the system is working like it was just installed.
I am reading a 21 degree temperature change on the incoming and outgoing air whereas it was averaging 12 to 14 degrees yesterday. it is now 94 degrees outside at 11.22 am. The relative humidity is now 55% indoors at this hour and I can see the water pouring down the drain pipe. Now why the system is working now, I cannot figure but guess. Here is what I did overnight and this morning and maybe someone can offer an opinion:

I shut down the Central Air and turned on a dehumidifyer in the basement. I turned on a bedroom window AC rated at 5000 btu and left the bedroom door open and placed my furnace fan on high.

This morning my Rh dropped from 60 to 55%.
Then I shut down the bedroom AC and the dehumidifyer and the furnace fan and let the house warm up to 79 degrees and I put a pot of water on the range to add humidity back until thermostate read 58% Rh. Then the last thing I did was reprogram the thermostat to read an offset of +2% Rh, so that thermostat now reads 60% instead of 58%. I waited to 10:00 am and switched on the Central Air. Within 15 minutes is when I noticed a big improvement in performance.

So I think it was either shutting down the Central Air that may have reset something on the circuit board or adding an offset of 2% Rh to fool the system into reading 60% instead of 58% Rh.
This latter change is also read by circuit board and may have sent a signal to the condensor to run faster.
What do you think?

rjordan392 08-10-2007 09:20 AM

Temperature Differance Over Coil Update:

I had to cancel the appointment with the HVAC man until I feel my system is malfunctioning again. My thermostat control allows me to test the central air system and I collected the data. I ran a 10 minute test each on high cool and low cool. here is the data:

High Cool:

Air Flow cfm. Begin 734 End 734
Coil temp. " " 77 F. " " 88 F.
Outdoor temp.
(at condensor) " " 79 F. " " 88 F.
Blower rpm. " " 685 " " 689
Static pressure " " 0.21 " " 0.22

The High Cool test was performed when the outdoor thermometer read 77 F.
The temperature differance over the coil as read on two duct thermometers was: incoming duct was 72 F. and outgoing duct was 53 F. A 19 degree differance.
So with a low morning temperature, it appears alls ok and moisture was being removed.

Low Cool:
This test ran immediantly after the high cool test.

Air Flow cfm. Begin 441 End 441
Coil temp. " " 87 F. " " 82 F.
Outdoor temperature
(at condensor) " " 88 F. " " 82 F.
Blower rpm " " 508 " " 508
Static pressure " " 0.16 " " 0.16

There was a increase of 1 degree F on the outdoor thermometer when this test was performed.
The differance in coil temperatures as read on the duct thermometers was:
incoming duct, 72 F. and the outgoing duct was 56 F. A differance of 16 degrees. I was getting less moisture removal. But this was better then when the outdoor temperature was 96 degrees F and the indoor Rh was reading 60% and there was no evidense of moisture removal.

Overall, it appears that looking at past performance, the system does not operate well under high heat conditions. I plan to repeat this test again, when the high heat and humidity returns and show the data to a HVAC man so that he has something to work with. Do you think this was time well spent in testing before I call him again?

pjpjpjpj 08-11-2007 03:12 PM

rjordan, where do you live? A lot of parts of the country are experiencing temperatures above their design criteria. In other words, where I live (for example), the design outdoor temperature is 95F with about 42% rh. But this past week, it has been 99, 100, 98, 97, etc. and the rh has been in the 50% range. Just nasty! At the building where I work, which is normally comfortable, the AC simply can not keep up, and it has been warm and slightly humid in the office in the late afternoons. Nothing you can do about that - sometimes mother nature exceeds "reasonable/prudent" design conditions.

rjordan392 08-11-2007 04:22 PM

I live in Philadelphia, Pa. The temperature now is 84 degrees at 5:13 pm.
I let the house warm up to 78 and the indoor humidity is now 58 Rh. I just turned on the central air.
This morning I was looking over the install booklets and I came across a section that stated that My system uses a 2 stage thermostat with a 2 speed cooling and it further states that the air conditioning relay disable jumper (ACRDJ) must be disconnected to allow thermostat control of the outdoor unit staging. Well, I located this jumper on the furnace control board and it is connected. So I will question this to the serviceman.
Unless he installed a single stage thermostat. Its called the Evolution control and I cannot find any referance at the Bryant website as to what type it is. Also this thermostat is the top of the line that Bryant company provides and controls everything without needing to go the basement to adjust anything.

rjordan392 08-11-2007 05:34 PM

Update for those following this thread.

The more I read the operational and installation booklets, the more I learn.

I learned that by lowering the thermostat 5 degrees below room temperature will force the outdoor unit to go into high speed. I tried it and now My temperature differance over the coil is 24 degrees and the water is pouring out of the evaporator and the time is now 6:25 pm and the Rh is 53%. Now thats performance.
The temperature at the thermostat is now 74 degrees and I will set it back 76 degrees which is where I normally keep it at. I also have the dehumidification set at 42%.

Now I will see if the system maintains low humidity after it cycles off and then back on a few times. I have a feeling that the system is not responding automatically to my thermostat settings to bring the humidity down and the only way I can do it is by forcing the system into high speed manually.

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