I have a ten year old carrier heat pump unit. I recently replaced the indoor tstat. the outside contact and the transformer. Had a tech put freon in the unit also. I have to problems one is the airflow is minimal coming out of the vents it has new air filter and I cleaned the inside and outside unit coils. And the second problem is the ac with not get cold.

If the outdoor unit is running the indoor fan should definitely be running. Turn power off to indoor unit. Put red green and yellow wires together behind the tstat with a wire nut. That is power (red), indoor fan (green), and compressor (yellow.) Turn power back on. This is bypassing the tstat and you should have indoor fan and outside running as well. If yes the problem is in the tstat, if no indoor fan the problem is in the unit. Good Luck!! Let me know!!

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Like have a clogged drain and the float switch is tripped. Check the drain line near the indoor unit for a piece with two wires. Remove switch and check for water or look in emergency pan under unit for water. DO NOT LEAVE SWITCH OUT, must vacuum clog free or blow out with compressed air.

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Should have a 5 amp fuse on red wire in between transformer and tstat. If not put one. This will protect transformer. Turn power off and take a good picture of tstat wiring. Remove all wires to the tstat. With the air handler wires join fan and red. (Likely green) let run. Then add compressor and reversing valve ( if reversing valve is energized in cooling ) which in most cases it is. Should then have cold air. Let run. If no problems you know it's outside of the machine. Tstat or wiring. Hook inside of machine all back up to tstat wires. Do the same thing with the tstat wire inside the thermostat. If no problems, must be bad tstat. Hook everything back up right. If fuse blows or transformer because you didn't put the fuse, then you know for sure it's the stat. Good Luck

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There probably isn't a reset button=magic fix. With it in heat pump mode and tstat set above indoor temp, check your outdoor unit to see if it's operating. If not, check all breakers to it. Can you see any ice accumulated on the outdoor unit? If it is running and not producing heat, turn the tstat to emergency/auxiliary heat. and the heat pump turned off to prevent damage. You'll need a service tech.

if your system is a heat pump you can switch to heat and see if coil outside gets cold while indoor blows warm air - then switch back to a/c - both coils should not be cold at the same time - low freon pressure / dirty coil / dirty filter / low air flow causes freezing

The majority of the time it is a contactor that its contacts welded together. Call service tech ask for free estimate up front. You can replace it yourself if you have a few electrical skills. To check to see if the contactor is the problem. Shut off power to indoor unit. This will kill control power to outside unit. If it still runs it is the contactor. If not you have a control problem. Tstat, shorted wires . Rus

If indeed your evaporator (indoor) coil is leaking, the best option IS replace it (it may not even BE repairable). If you live in the USA and your furnace is getting old, a new ultra high efficient SYSTEM that qualifies for the tax credit would probably be a better option (Obama will pay 30%).

YOUR the first person that has gave enough information to help in a WHILE THANK YOU SO MUCH!!

Start all over from first
I'm betting that you need a fuse in both sides of the transformer until you find the real reason they burn up.

A solenoid valve that sticks can cause the transformer to blow but so can a lot of other things, namely anything in the control circuit that uses the 24V power. A relay or contactor that doesn't pull in or a defective defrost control, a shorted wire from the thermostat.

I'm wondering if you have what we call a package heat pump meaning the both the indoor blower and out door compressor & fan are in the same section out side? OR is your a split system with an indoor section and an outdoor section?

I'm betting on the split section. In some miss-matched systems (like a Lennox indoor and a GMC out door for example) Some of the origonal Lennox heat pumps had an out door and an indoor transformer. If these trans formers were not "phased" together it could cause a problem like your having. Now you just have it in the heatign mode if I read between the lines correctly. So it makes snece that it's something with the heat. The out door unit can opperate withits own 24v but if you have back up heat inside (gas or electric Im thinking you have electric) the indoor section will come on atfter a few more degrees of heat loss (2-4'F). This is where the transformer inside will buck the one outside and somethjing has to give. The weakest point.

From what ive been told by some of the old hands I've been around if the high volt side burns out look for a low volt problem if the low volt burns out look for a line volt problem.

If this has 2 transformers like I suspect try the fuse on both sides but remember the one is hot and will remain hot all time on 220V or 1 leg of it or it might remind you. To phase these transfoprmers I believe you swtich the main lines L1 & L2 at either of the transformers. Now 1 more thing the indoor section may be using ground on the low volt side as a path for 1 side of the transformer. I believe you will ahve to do same for the other transformer too.

Hope this helps Id really like to know what you find and do.
Please ask more and you give such detail I can follow you with little trouble. Please rate me as high as you can and good luck.

unit should be locked out on low temp and your electric heat should be running. is your installer a service tech or just an installer that could also be the problem if he is a service tech it would work correct when he left

Depending on the age of the unit it could be several things, does it have a circuit board? Contactor could be bad, freon leak if it has a low pressure switch, burnt wires, connections, etc. Do a complete visual and check for 24 volts, does the indoor unit run? Transformer may be bad.... No indoor unit - no outdoor unit, most of the time the outdoor unit gets its 24 vac power from the indoor unit which runs them both, look for fuses (like car fuses)..