Air Conditioner & Heat Pump Diagnostic FAQs-2

Q&A help Fix Air Conditioners & Heat Pumps Set#2

A/C or Heat Pump Supply Air Too Warm FAQs

Air out of Supply Vents is Not Cool Enough

Got home today and the temp on the thermostat said 78 we have it set at 74 and it has now gone up to 79.

The air coming out of the vents is cool but not cold like usual what could be the cause of this? On 2012-07-05 by Tina -

Reply by (mod) -

Tina: regarding "air coming out of the vents is cool but not cold like usual" - if the home is very hot it is possible that it could take a while for air coming out of the supply vents to cool down - the system has to cool the whole duct system as well; It'd make sense to check for a dirty air filter or an ice-blocked cooling coil too.

But if the "cool air" supply never cools off, and if the air flow rate is not also reduced and those blockages I just named are not present, it's time for a service call.

You might want to review the more detailed advice

at LOST COOLING CAPACITY

 

Heat pump sometimes blows warm air when in COOL mode

I have a heat pump and it periodically blows warm air in AC mode, this happens several times a week. If I turn tje unit off for about 15 mi utes and then back on it works fine. We've replaced rhe brackers and fuses, it has clean filters and the compressor is running. Please help! On 2018-06-25 by Jackie

Reply by (mod) -

if your system is switching to heating mode and you're not calling for heat I suspect there's a control board problem

Your service tech will probably first rule out a control board problem that is blowing warm air in cooling mode during a deicing cycle.

A/C Heat Pump No AirFlow FAQs

Crawlspace (where ducts run) is cold but the house above is hot

I had a new central air unit installed last summer. If it's hot outside, my new system can't keep the house at the temperature set on the thermostat. 74 degrees.

To keep the temperature from exceeding 76 degrees I have to use all of my ceiling fans, a table fan, and the central air unit

However, my crawlspace, where the duct work is located is freezing. In addition, during routine maintenance this Spring, the technician found the unit a full pound low on refrigerant.

I have had three service calls but each time I am told that the system is fine. I've lived in this house for 12 years and have never had this problem before. Any ideas? On 2012-07-03 by Anonymous

Reply by Mod - look for disconnected or leaky ducts in the crawlspace

Anonymous: if the crawl area where HVAC ductwork is routed is freezing cold and the occupied space of the home is too warm when your A/C is running, I suspect a supply duct leak into the crawl area; Inspect the ductwork carefully for damage.

 

No air coming out of A/C supply registers

The A/C unit is running outside but no cool air is blowing through the ducts. We put the thermostat temperature lower and nothing happened. If the thermostat is temp is put higher the the actual room temp, the A/C unit outside does stop.

Also tried to run just the fan, but it did not work (does not start). Yesterday the A/C unit worked without the fan, after letting it off even with turning off the breakers for a while, it worked again through the night. This morning the blower stopped working again. On 2012-09-04 by Ken

Reply by (mod) -

Ken as you have no air coming out of A/C supply registers it sounds as if the indoor air handler blower fan is not running, or if it is, that something (iced coil or dirty filter or crushed or disconnected ducts) are blocking air flow.

I'd start at the top DUCT & AIR FLOW PROBLEMS and go through the diagnostic suggestions there

and at AIR FLOW TOO WEAK

Condenser Unit Fan Speed FAQs

Slow Condenser Fan Problem Diagnosis & Repair

I have had this problem with my AC unit for some years now. techs have been out several times for free inspections, and nobody seems to see anything wrong other then try to sell me a new unit.

That costs $1000's. So here is the weird thing. When the condenser fan started to go out slowly but surely, for some reason the AC was working better then ever!

Cooled on the hottest days. I know the condenser fan was running slower until the tech came to replace it.

But now that he replaced it, here we are again with warm air. Or shall I say cool air, but not really cold.

Someone told me maybe the RPM rating of the condenser fan is too high, and over cooling the coils. I never heard of that. Or theoretically how is this possible?

But one tech guy told me that the outside condenser coils needed to get warm enough for efficient cooling to occur.

Over cooling them won't allow the exchange to happen properly. Is this why we have been living with the cooling efficiency AC unit? On 2012-06-17 by Anon

Reply by (mod) - Condenser RPM and Condensing coil warmth - Illogical claims?

Condenser RPM question:

Thanks that's an interesting question and not a hypothesis I've come across. At least part of it makes no sense to me whatsoever, in particular, and reading your comment to refer to the outdoor condenser FAN unit not the compressor motor itself:

"But one tech guy told me that the outside condenser coils needed to get warm enough for efficient cooling to occur."

Think about what is happening in the outdoor compressor/condenser unit: the compressor condenses low pressure refrigerant gas into a high pressure high temperature refrigerant gas. That high pressure high temp gas enters the condensing coil.

The outdoor fan blowing air across the coil transfers the heat of the high temp high pressure gas to outdoor air, AND in the process condenses the gas back to a liquid refrigerant that is then sent over to the indoor cooling coil.

Making the outdoor condensing coil hotter would not improve its performance, it would harm it, in general.

There could be something else, odd, going on, and it doesn't sound as if you've had a clear onsite diagnosis.

Some fans can run at more than one speed or even variable - but usually at the indoor air handler not the outdoor unit.

A bad motor, voltage, or control can cause the outdoor condensing fan to run at the wrong speed however.

It may be worth looking further for a problem with refrigerant metering equipment at the indoor air handler/cooling coil, or the system could have an improper quantity of refrigerant charge;

I am SPECULATING that artificially slowing the delivery of liquid refrigerant back into the indoor equipment (slow outdoor condenser processing) might mask an indoor refriterant metering problem. Keep us posted, what you learn will certainly help others.