Laymans way to check cooling capability?

Old 07-11-14, 02:53 PM
Thread Starter
Join Date: Mar 2007
Location: Jupiter
Posts: 180
Received 1 Upvote on 1 Post
Laymans way to check cooling capability?

I'd like to check the efficiency of the AC units myself to try and anticipate any leaks, not sure if this approach will pass muster, any comments apart from checking in with a psychiatrist:

4PM 97 F outside temp., both units are in a similar shaded location, test as follows with an oven digital thermometer, both units running and both have same, new insulating foam on the large pipe.

Both small pipes going into the units - 109 F

Large 3 ton unit - 'hex' brass nut on large pipe measured - 63 F

Smaller 2.5 ton unit - 'hex' brass nut on large pipe - 82 F

Both units are cooling, the 3 ton was in a prolonged run cycle at the time dropping the upstairs by 2 F, whilst the smaller unit was maintaining the downstairs.
If this approach is baloney, what can be done by the man in the street to anticipate any Freon loss, apart from waiting until it doesn't cool at all and possibly have damaged the unit in the bargain.

Old 07-11-14, 03:16 PM
Gunguy45's Avatar
Super Moderator
Join Date: Dec 2007
Location: USA
Posts: 19,281
Received 6 Upvotes on 6 Posts
You are probably better off measuring the "split" (or I think it's called Delta-T?) across the evaporator coils. The simple way is to measure at a return and at the register furthest from the unit. A simple thermometer like this [ATTACH=CONFIG]34619[/ATTACH] can be used just by inserting in the grille.

Ideally, you do it by drilling small holes in the air handler behind and ahead of the evaporator coil. They can be easily resealed with aluminum tape. 16 degrees is adequate, 20 is better...but that's the normal range.

The temp of the pipes outside can vary somewhat based on outside temps and humidity and load on the unit I think. I believe the split should remain pretty constant.

The system is sealed so any leak would degrade performance and probably produce longer run times to maintain temps, until it gets so low that the coils start to freeze or the compressor shuts down.
Attached Images  

Thread Tools
Search this Thread
Ask a Question
Question Title:
Your question will be posted in: