Church needs help York A/C 7.5 ton

Thanks for looking at this post. Our church has an 18 yr old York 7.5 ton unit. Its been giving us problems for a few mos now.....we can't afford a new unit...so we're going to have to try to fix this one. We've had several a/c companies look at it.....but they just temporarily fixed it. Mostly with freon. To get it to work we have to spray the coils down with water....it works just for a few mins then....back to warm air. We don't think its a compressor problem.....one man said it has 300lbs of pressure..whatever that means. The last people who looked at it.....cleaned the coils...and it worked better but not good for a few days. Any help would be deeply appreciated thanks,

Alan

 

High head pressure (the 300 lbs) would indicate high ambient temperature, dirty condenser coils, impaired airflow or non-condensables. Is the fan turning the right direction and do you have proper airflow? No bushes too near the condenser? Nothing impeding the airflow in any way?

Other than external cleaning of the coils and trimming any bushes impeding airflow there isn't much a non-certified person may do.

 

Thanks for the quick reply.....no bushes or trees around the unit at all. And the last a/c man just cleaned the coils (last week) We're going to get another a/c co to look at it...we just want to know what to tell him......and want to be able to make sure they fix what needs fixing.... What constitutes...high ambient temperature is there a normal range? Thanks again,

Alan

 

In the case of 300 psi (lbs) pressure if everything was working properly it would correspond to about 120 degrees ambient. (more or less) If your ambient air temperature is less than 100 degrees F. then the head pressure should be around 200 to 220 psi. While it is not possible to diagnose a problem with only a head pressure reading my gut tells me it is overcharged with refrigerant, the condenser is dirty, there is air (non-condensables) in the system, the filter-dryer is plugged, the expansion valve is partially plugged or a combination of these problems.

Note, the pressure-temperature relationships I posted are for R-22. If your system is fairly new it may be using R-410A and if so, the 300 psi reading may not be abnormal.

 

Thanks...for the info...its an older unit so R 22 is probably still used in it. I think...you've steered us in the right direction. Will tell the deacons tomorrow....so they can have an idea of possbile problems..before the a/c repairman comes out. I kindof think it may be a combination of these problems...since there's been several different. people who's worked on it. Thanks again,

Alan

 

Is this a split unit with the air handler inside and the compressor unit outsdie? if yes, feel the smaller uninsulated tube at the outdoor section when the unit is running. Is it- about he same as oudoor temp? warmish? hot? HOT? burn thy hand hot?

 

My guess would be that someone seriously overcharged this unit to keep the evaporator coil from freezing. I would guess the evaporator coil or filter is plugged or possibly a bad blower belt on the air handler/furnace causing an airflow problem. The compressor may be shutting down on the thermal overload or bypassing on the internal compressor relief causing the warm air. The right service tech should be able to correct this problem. JMO

 

Furd's magic hammer hits the nail head square as usual.

Skip brings up a very valid point. Who knows how many people have put gauges on this thing. "Add gas, just add some gas".

IMHO. If the outdoor coil was cleaned with a pump-up garden sprayer, it isn't clean. Clean it with a coil gun. Reclaim all the R-22 and start over. The unit should have a base charge listed on it's data plate. Start there and add charge until the charge chart specs are met.

Obviously after the coil cleaning this is not a DIY. But does offer points to bring up with the actual technician.

Good luck!