Home AC question - PeachParts Mercedes-Benz Forum

dannym · #1 05-09-2009, 10:19 AM

I was out checking the pressures on the home AC. R22 system.

The low side was at 75 psig which corresponds to about 45 deg F.
The high was hard to tell because from 120 psi - 250 psi it says RETARD. I don't think this matters with R22 does it? I thought R22 operate at around 200 psi on the high side?

Anyway, I'm thinking it may be overcharged. Shouldn't the low side be around 60 - 65 psig?

Outside temp is around 80. Also I'm getting around 55 degrees out of the vents.

The reason I'm checking is the back rooms always seem to be hot. Any help or advice would be appreciated.

Thanks!

Danny

jplinville · #2 05-09-2009, 11:20 AM

I'm willing to bet that your back rooms are furthest away from the system. That being said, dampen the front rooms some to force the air to the back rooms.

The pressures sound ok...

OMEGAMAN · #3 05-09-2009, 02:18 PM

never worked with R22 but I would imagine retard means too much pressure. Have you cleaned out the condensor unit this spring? If it's plugged it could cause excess pressure. I find on cars that compressed air cleans better than water for condensors.

Matt L · #4 05-09-2009, 02:20 PM

Quote:

Originally Posted by OMEGAMAN

never worked with R22 but I would imagine retard means too much pressure. Have you cleaned out the condensor unit this spring? If it's plugged it could cause excess pressure. I find on cars that compressed air cleans better than water for condensors.

That's just too much pressure for his service gauge. My low-side gauges all say "retard" at the high end of the scale, where the needle movement is mechanically restricted. They are very inaccurate at that point.

OMEGAMAN · #5 05-09-2009, 02:24 PM

Do home a/c systems have a cutout switch for too much pressure? How about too low?

Matt L · #6 05-10-2009, 10:16 AM

I would expect so, but I am not sure. None of my window units seem to have anything but an evaporator temp sensor.

mgburg · #7 05-10-2009, 02:10 PM

I've been dealing with A/C issues at work for the past few years...

The service guys tell us the most important thing in A/C health is keeping the fins of the compressor CLEAN...run/spray water in a back-flushing mode (against the air-flow) to remove all the air-borne fluff, grass and pollen that's clogging the fins/boas (that fluffy, feather-boa-like stuff), being VERY CAREFUL not to fold over the fins (There are commercial fin-combs you can buy to straighten out folded-over fins...works great on car radiators, too!!)

The heat's not being removed, the head- and tail-pressures will increase to the point that if there's no cut-off switch for too much high-pressure, the compressor will overheat and (hopefully) a shut-off thermal switch will kick in...depending on the cheapness of the compressor head part of the system, you may not want to find out that little secret 'til you talk to your serviceman on that.

If your compressor has never been cleaned, there are commercial grade fin cleaners out there...FOLLOW THE LABLE DIRECTS CAREFULLY! The cleaners are caustic, but they'll pull a ton of stuff out of your fins even AFTER you thought it was clean. After doing the cleaning with the cleaner about three or four times (not all at once, over a period of months), you'll be able to just rinse the fins with a regular garden hose and spray tip...just reduce the useage of the cleaner to every other two or three rinsings...

Cleaning the fins takes care of about 85% of the problems...the rest is usually a small leak in a connection someplace or a hole that developed along a part of the line near the compressor that wasn't properly routed and may be rubbing on the frame or metal-work of the housing...just look around the tubing coming and going from the unit for little signs of "something is just not right" and you'll probably find something, or not. Don't go blame the installer for that type of problem...I've had lawn-mowing persons "bump" the condensor unit, or its frame, and that type of movement will be enough to cause one of the lines to re-align itself against something metal...if that's the case and see something like that, let a serviceman come in with a "sniffer" or leak-find fluid and let them handle it from there.

Now, if you're undercharged, you'll find that the coil in the air handler will probably "ice-over" - call the serviceman to check that out...but one thing you can do to save the call on that, first!

Open ALL REGISTER VENTS to be sure there's enough air-flow over the coil to keep the coil from freezing solid...too low of air flow will appear as an "undercharged system" when in reality, you have someone in the house that's too hot and has shut all the other vents down to get more cold in their area. (I learned that the hard way! ($203.00 the hard way!

)) So be careful closing down vents to transfer cold to other areas that aren't cool enough...in those cases, it's probably better to have a "booster-fan" installed in that branch of the ducting system to assist in getting a better balance of cooling throught the whole home.

Good luck fixing this...just remember...a little effort on your part keeps your bucks in your pants...

dannym · #8 05-11-2009, 08:12 AM

I've cleaned the evaporator coil 3 times in the past year and a half.

I shot water from a garden hose through the condenser coil. I saw it coming through the inside of the coil and did flush out a lot of leaves. I'm sure it's clean but I think I'll remove the metal from around the coil and give it a good cleaning with coil cleaner.

I did play around with the vents and it worked a little but not as much as I hoped.

I think I'll go up in the attic and check the insulation. But I was thinking 55 degrees from the vent may be high? I was expecting 45 degrees.
If people can take air temps from their vents & post them here I would appreciate it.

Danny

cjlipps · #9 05-11-2009, 10:32 AM

You don't state the return air temp (basically room temp) but it was explained to me years ago by an experienced HVAC contractor that a 16-20 deg. delta T from the return air to the register output is good. IOW, if you have 55 deg F with a 75 deg room temp you are doing well.
Don't know what to tell you about the pressures. You might check the evaporator coil to ensure maximum airflow there.

pj67coll · #10 05-11-2009, 10:41 AM

The rooms that are the hottest will be furthest from the system with the longest ducts running thru your roof. I have exactly the same problem. I want eventually to install a second unit for the west side of the house because of that.

- Peter.