Another AC question from Texas!

[HtTXLdy]

First let me begin by saying I'm definitely NOT a DIY-er! Just someone who also lives in Texas (Dallas area) and has questions on AC operation and what I'm being told by my AC repair company. As a single parent I don't have time to do a lot a research so any advice/clarification you can give will be a great help!

About my system: I live in an 11 year old home. It is 1880 sq ft. The AC system is original. It is a Payne PH10JA042-C. I'm not sure of the tonnage but from what I've been able to determine from the net that Model is a 3.5 ton unit. If anyone has other information about the tonnage, please let me know.

My question is in two parts:

First, my AC went out a couple of days ago. The repair tech said the motor start capacitor in the outdoor unit had gone out and replaced it. This same part went out three months earlier in April so was covered by warranty. He said the reason the capacitor was going out was that the condenser "had a problem". He cited a strange noise which I can't really hear. He continued to say that the pressures looked good but showed me a device connected to a thick pipe going into my house. He that he said was reading the temperature of the coolant going into the house. The reading was approx 87 and he said it should be around 55 to 65. This indicated that there was a problem with the condenser and it was not working efficiently. He said the entire outdoor unit should be replaced. He also said that the inside coils should be replaced because a new type of refrigerant is required by the gov't. The repair company called later that afternoon to give me a quote that shocked me.

Here are my questions from the first part: with the capacitor replaced, my house cooled from 91 to 77 degrees from 2 pm to 10pm. How fast should the house cool? Is 8 hours what would be expected or would it be more like a couple of hours? Also if the temperature of the refrigerant is 87 degrees how would my house ever cool down to 77 degrees? That doesn't make sense to me. If I replace the outdoor unit do the inside "coils" need to be replaced as well? The quote the company gave includes a new thermostat. Why do I need to replace my thermostat when the existing one works fine?

The second part deals with how well my system is functioning. I really think alot of this is covered in the post earlier today by SWTSAE. I have a similar situation. My ac will run continuously from about noon until 10 pm. I keep it set on 78 but around 4 pm the temp will creap up to about 80 and stay there until the sun goes down. From reading the post I reference it appears that I need to take a look and the "seal" of the envelop with thing like caulking and radiant barriers. Are there reliable companies that will for fee come in and evaluate a home and make suggestions? Can anyone suggest links on the web where I might learn about this myself? Thanks to everyone who posted info in SWTSAE's question; that helped me a lot.

Also can this unit be used as a heat pump for cooling in the summer? I downloaded the manual and it says the compressor is "designed specifically for heat pump duty, with energy efficiency during heating and cooling operation." Would that be more efficient? The tech asked something about this yesterday. The thermostat (mfg Hunter but couldn't find model) has three settings: normal, heat recovery and emergency heat. In the winter I know I can use natural gas or use as a heat pump. I set it on normal to run as a heat pump and on emerg heat to use nat. gas.

Thanks in advance for any information you can share.

[motoguy128]

First, what was the tempeature outside when he took him measurements?

Maybe the pros can jump inhere, but a high temp on he vapor lineI thought could indicate that the system is overcharged or there's another issue.


The air inside is not cooled directly by the refrigerant. A A/C sytem works by taking advantage of "phase" changes. Meaning absorbing and releasing heat by going from a liquid to a gas and back. Remember how the temperature of ice stays 32F until it melts to water? and how the tmeprature of water stays 212F unitl it boils? WEll the A/C works that way. It cools the indoor coil by allowing liquid to vaporize. Then hte comrpessor compresses the vapor. the compressed vapor is cooled in the outdoor condenser and becomes a liquid again. Hence the terms evaporator (indoor unit) and condenser (outdoors unit).

Hope that helps. The pros on here might make some suggestions what other issues it could have. But I agree with the tech that 87F on the vapor line is not generally good. But WHY it's 87F, could be many different things.

I would question why it keeps burning up capacitors? I think that indicates the compressor is working too hard. I would guess something is blocked/restricted, or maybe the unit is overcharged.

With the realy really hot weather TX has been having, I think it somewhat normal for a properly sized system to fall behind in the afternoon. The reality is that most people have oversized equipment... so their house stays cooler, but in more mild weather it can be very damp indoors.


If you have rasonably low electric rates, then it cheaper to run the het pump as low as possible. If you have higher electric rates or very cheap gas, it might only be cheaper to run the heat pump above perhaps 40 or 50F. Heat pumps are more efficienct the warmer it is outside.

[Shophound]

91 to 77 degrees in ten hours is about a 1.4 degree drop per hour. That's about a normal pull down rate for residential air conditioning.

If you want quality information on how to make your building envelope perform better, you'll likely need to hire and pay a certified energy rater/auditor to obtain a plan of action. Spreading caulk around won't do much good if you spread it around in the wrong spots. Knowledge is key to energy reduction and comfort improvement.
Check with your utility provider if they have assistance with energy auditing of your home. Even there, if they want to send some high sales pressure pushy guy who does a perfunctory inspection of your house and wants to sell you a bunch of stuff, I'd look for a different person, one who is mainly interested in identifying the weaknesses in your envelope, and delivering to you a feasible strategy to address them.

There is always someone out there eager to sell you something. Nothing wrong with that, as long as it fits in nicely with an intelligent strategy derived from real time observations.

[larrytbm]

From reading the post I reference it appears that I need to take a look and the "seal" of the envelop with thing like caulking and radiant barriers. Are there reliable companies that will for fee come in and evaluate a home and make suggestions? Can anyone suggest links on the web where I might learn about this myself?

Call your local utility company, some will do an energy audit for free and there may be funds available to help with making energy improvements. They can also help you find a company accredited to perform the work.

[HtTXLdy]

First, what was the tempeature outside when he took him measurements?

But I agree with the tech that 87F on the vapor line is not generally good. But WHY it's 87F, could be many different things.

Thanks for your reply and help. Just a follow up question:

Outdoor temp was probably around 102.

Is is possible to measure 87 on the vapor line and have the house cool to 78?