Gas and Oil Home Heating Furnaces - Air Conditioning Problem

We have an older Rheem unit on the roof. It is a combination air conditioner and heater. It is about fifteen years old and the serial numbers are not even visible anymore. Anyway we bought the house a couple months ago and it checked out fine but now I turn on the unit and it will blow cool air for about 20 min or so and then no more air but the unit above will still be humming along. It does not go back on. Today it showed it was 90 degrees room temp and turned it on to 80 and it still did the same thing. Does not shut off because it cooled the house down because it is no cooler.
Help!!!

Its alittle hard to tell what your dealing with but my guess is that you may be freezing the indoor coil. If thats the case the first thing to check would be the filter and outdoor coil which is on the roof top unit. The filter needs to be clean and vents opened in the house. The coil on the roof top unit will be located behind stamped louvers on the unit. They will often go for years without being cleaned. Take a hose up with you and wash with strong pressure in a horizontal back and forth direction starting from the bottom working your way up to the top. Pay particular attention to the corners, the outside grill is square and the coil behind is rounded. Alot of dirt will collect there. Once done restart the unit and see what happens.

There are other reasons for freezing (if thats the problem) but this is the starting point.

One other thing to notice is wether or not the indoor fan is going south. If the fan stops during operation the same thing will happen as you've mentioned. To access the fan you'll have to take off one of the top panels. The panel will be to the left of the condenser (outdoor) fan compartment. If the unit fails after cleaning, remove the panel and notice if the fan is still running. If it is, put the panel back on. Don't let it run for long peiods of time without it. If not, its probably best to contact a local contractor.

Thank you for your reply Phil. The filter is clean, we checked that last night. There are seven vents for that unit and only two are closed. We will try the cleaning in then next couple days and let you know what happens.

Okay, I opened to top where the blower unit is and found about 1/2 inch of lint laying on top of the motor. Also lots of dust on the inside surface of all the insulation. Also a layer of black lint on the inside of the indoor coils (unit side). The downdraft or house side of the indoor coils was clean. I thoroughly cleaned the outdoor coils from both sides, took a coil brush to the inside of the indoor coils and got as much of that black lint off as I could. No way to really clean through those coils with a blast of water because the vent being on one side and the unit being on the other with very tight tolerances. We turned the unit on this morning and the blower motor stopped working after just five minutes. I pulled top of unit and inspected again, found some kind of control switch with temperature degrees on it ranging from "unit off" to "120 degrees". Played with the adjustment but the motor still didn't work. HELP!!!

If you have that much dirt your motor has bad bearings. Running overheated for extended periods of time draws oil out of the bearings and wipes them out. Have it replaced and the blower wheel cleaned. The indoor coil will need to be cleaned also. Use something like Simple Green to spray the coil and a pump sprayer to wash it off with. Provided the charge is proper, you should be back in business when finished.

Also, if it is your motor, be sure and replace the capacitor.

Thank you for your help. Both of you. Phil, I wasn't sure if you were talking about replacing the motor outright or just the bearings?

Replace the motor outright. A good technician would never replace a motor without the capacitor, so they both go together.

I work in a correctional institution here in California. I talked to a couple of the HVAC guys there too. They seem to think that the motor might be overheating and shutting off for some reason. The only thing I haven't cleaned is the inside coils. I will get to that sometime this week. In the meantime I am not running it. I'm not sure if the bearings are bad because for the amount of time the blower motor is going it is not noisy at all. The unit is under our home warranty but I'm sure that they will probably find it to be pre-existing and therefore not covered, so I am going to try to fix it myself, if possible.

Bad bearings rarely make noise. Their actually a bronze bushing which usually becomes tight from excess heat and gunk buildup. If your system was noted as properly working during the home inspection, your home warranty should take care of it. You may have to raise the roof with them, but they should take care of it. For the cost of the deductable, its worth a try.

Save yourself grief. "You bought the house a couple of months ago and it checked out fine". YOUR PROBLEM THEN IS NOT "PRE-EXISTING". But, are you sure though that the home warranty included the AC unit?

I called the home warranty service and had to pay $35.

Let us all know what fixes the problem.

This Antelope Valley heat is unbearable.

Just wanted to let y'all know that I finally did call the home warranty folks. Yes, the air conditioner is covered like I thought. Anyhow they came out a couple days ago (I had to pay a $45 service fee). They checked the unit and the blower motor is bad. They are replacing it this Friday. Hooray!!! God last week was horribly hot but we survived. We do have another unit at the other end of the house which saved our bacon. Thanks again for all your help.

Well, the guy came out today and put a new blower on the unit and it did the same thing. Now he says that it is a relay switch that is the problem. Does this sound right? I really hope we have the problem nailed down now. Just thought I would let you know. Any comments?

It might even be a weak circuit breaker(s) that kicks the system off when it (the breaker itself) overheats.

I hope he left the new blower in.. hee hee. Rather than properly testing... he "tube jockied". Just go brew some pruno and enjoy the heat... ha ha.

The more new parts they put in, the better for you!!

Well, they came out and replaced the relay also and now it seems to work fine except for the fact that it still does not have much pressure coming into the house. We still need to clean the indoor coils is my guess.

Phil, you mentioned cleaning the indoor coils with simple green and a pump sprayer. Do we not need to worry about getting all that gunk in our duct system? These things are absolutely coated with sticky grime. It looks like it will take a ton of water to get them clean?

My husband is thinking of tearing the whole unit down which is a real hassle, just so he can scrub these coils. I don't think that they have ever been cleaned the life of the unit.

Any suggestions?

By the way, they did leave the blower in!!! We have a new blower, capacitor and relay.

1) It sounds like the insurance company is screwed. (Not your fault though.)

2) Coil inspection:
......a) The surface can be clean but the fin spaces may be choked with dirt. Open the indoor coil box YOURSELF and shine a bright 60-watt light on one side of the coil. Use a mirror on the other side to see whether light will pass through the coil fin spaces.
.......b) You should be able to see slots of light coming through the fin spaces. It is all but impossible to deep clean the coil without cutting the lines and removing it from the house. It is less work to install a new coil.

3) Coil cleaning:
......a) You will need a wire brush or a stiff bristled toilet brush, flashlight, hand mirror and an assortment of screwdrivers. Latex caulking is good for resealing the coil box after you are done. Latex caulking washes off with water and it won't bond so tightly that you cannot get it off nest time.
.......b) Try to lift off the surface dirt with a wire brush, be careful not to push dirt deeper into the coil and not to bend the fins. Use the mirror and flashlight to look through the fin spaces for embedded dirt. If it is dirty inside, washing with a stream of water at high pressure can remove much the dirt but often leaves some. You see the obvious problem with that.
.....c) Wash the coil with liquid laundry detergent or a coil cleaner and water using a pump-up sprayer of some kind. A water hose can be used with extreme care not to drip, spill, or overflow the pan. Have the Power OFF. Keep the water away from all electrical components. Backwash the coil to force the dirt out towards the direction from which it entered. Flush the dirt out of the drain pan and drain line at the end of your coil cleaning.
.....d) If the coil interior is really jammed with dirt, you will probably not be able to get enough force without a pressure washer (like at a carwash). In this case coil replacement is the best option since aggressive coil cleaning cannot be done inside of the home without an unacceptable risk of water damage. Thus the labor cost of cleaning is greater than the labor cost of replacement.
.....e) Clean it regularly/yearly to keep the dirt from building up inside of the coil. Many air conditioning companies neglect to clean the indoor coil because of the difficulty and risks involved.

4) Filters are a great long-term investment. You let the filters catch the dirt and throw it away. This prevents future coil cleaning expense or work and reduces energy waste.