Help with household heatpump-No A/C

[duckloads]

I looked at a friend's heat pump over a month ago. She has no A/C. I was able to push the contactor in and the A/C worked just fine. I looked at the pressures, and they looked fine. This was Memorial Day weekend and no parts stores were open. I really didn't know what was wrong anyway. I told her the problem didn't look terminal and shouldn't cost to much to have fixed.

I just learned that she still doesn't have A/C. Are there any HVAC controls people on the board who could direct me on what might be wrong? The heat index in North Alabama is around 100 deg F. I don't mind at all buying the parts.

Thanks

 

[cshoff]

When you pushed the contactor in, the compressor came on, pumped, and had "good" pressure you say? What kind of hi and low side pressure readings were you getting?

If the compressor comes on and you are getting good pressures with the contactor manually held in, then it's most likely a low-voltage problem. Possibly the low-voltage transformer has gone out, or perhaps a fuse in the low-voltage circuit (will probably look like an old automotive style, glass fuse) has gone out, the thermostat may be defective, a pressure control may be bad, or the solenoid on the contactor itself may be bad.

I generally just start testing voltage, and where the voltage stops is usually where the problem lies. BTW - Your low-voltage circuit should be right at 24 volts +/-.

 

[badam0112]

I just had to have a capacitor replaced on our heat pump. Is the fan blowing on the unit outside?

Also, Is there a re-set button on the condensing unit that might be tripped?

 

[jmcghee]

set thermostat to cool, set temp on stat way below room temp. check for 24 volt at contactor. if you do not have 24 volt at contactor you have a t-stat or t-stat wiring proplem.that sounds like what you have .if you want to call ,feel free, will try to help over the phone. you must have a multimeter and know how to use it, jim mcghee 302 463 4786

 

[duckloads]

Thank you all. I don't remember exactly what the pressures were. I checked the pressures of my own house A/C before I looked at hers, and they were very similiar. Nothing comes on until I hold the contactor in.

I left something out...........There was a relay mounted a few inches away from the contactor. It had a clear case and one of the contacts inside was physically burnt. I don't have any idea what it goes to, but If I can find a supply house open in the morning, I'll replace it.

Jim, thanks for the number. I'm on Central time. What time zone are you in? Yes, I have a multimeter, I just don't know what I'm looking for.

 

[MK]

Yep, sounds like no 24 volts to the condensor. If the clear relay
looks burnt, but the compressor starts ok when you punch the
contactor, I doubt that is the real problem. It might effect other
operation though. IE: reverse valve for heat, etc..
I wouldn't worry about it quite yet. You need to see why there is
no 24 v to the contactor. Look to see if there is a 3rd party
delay module mounted inside. Those can flake out and you will
lose your 24v. They are wired in series across one of the low
volt wires.
If no delay module, start tracing back to the furnace.
There are two wires that run from the condensor to the furnace.
If you get voltage where they connect to the furnace, but nothing
outside, there may be a break in the wires.
Some systems use float switches on the drain pans which cut the 24v
to the outside unit. Being as it hasn't run in a long time, the pan should
be dry, and the switch is closed. But worth a look anyway. They can get
bumped down, and that would kill your voltage to the outside if the
float is mashed down onto the pan.
If the T-stat uses batteries, make sure they are good. Dead batteries
on digital stats can cause really funky problems sometimes.
Need to know if the fan comes on inside..
If the fan is coming on when they set to cool, you know the
transformer and furnace fuse and fan "green" wiring is good.
You are right.. This should prove to be a fairly minor problem
as far as problems go.. Just need to find out where your losing
the low voltage to the condensor. Maybe Jim can help you find
that over the phone. It's quicker than trying to explain how to
do it using text.
BTW, it is possible that there is 24v to the contactor, but the
windings in the contactor opened up. But that doesn't happen
near as often as losing the 24v due to other reasons closer
to the furnace.
It's meter time to be able to tell for sure. :/

 

[duckloads]

Good stuff thanks.

"If the T-stat uses batteries, make sure they are good. Dead batteries
on digital stats can cause really funky problems sometimes.
Need to know if the fan comes on inside..
If the fan is coming on when they set to cool, you know the
transformer and furnace fuse and fan "green" wiring is good."

I'll check the batteries. I don't remember the t'stat type, but wouldn't that be a hoot if the batteries were dead.

YES, the indoor fan comes on with t'stat demand for cooling OR heat. I know that the heat strips DO work in the indoor unit with a t'stat call for heat. I don't remember if the compressor ran in heating mode.

Most of the supply houses have gotten really weird around here about selling parts to the public. Contractors seem to be afraid that people like me that are just trying to help someone will hurt thier business. That stinks. Anyway, hopefully I'll be able to find a supply house open. I'll print all this info out and take it with me.

Question, Is the 24v ac or dc at the contactor?

 

[MK]

The 24v is AC. If the fan is going that is a good sign. At least
the transformer is good. Sounds like a wiring or stat problem
pretty much. Heck, it could be something as simple as a wire
pulled lose from the transformer terminals.. You might get lucky and
not have to buy any parts.
Yep, most wholesale distributors don't sell to the public.
Some do though, although they might bump the price up a bit.
If they ask, tell em you are the homeowner. Don't tell em
you are fixing it for someone else.
Some stuff like T-stats, you can buy at Home Depot, etc.
I also think you can buy quite a few parts online, although
that would take time, and be kind of a pain..

 

[Spotteddog]

Once again,
What MK said!

 

[duckloads]

"Heck, it could be something as simple as a wire
pulled lose from the transformer terminals.. "

Question...Where do I find this transformer?

 

[TAC]

In Michigan our electrical service providers have what is called interruptable service. They put the central air on a separate meter and they can remotely interrupt your AC service for short periods of time during high demand peak usage times. If they have that in Alabama, you might look for trouble with that device as well.

 

[MK]

It will be the terminals all the low volt wires connect to
on the furnace/air handler.
Some use a plate mounted to the transformer.
Some use a separate terminal post. Just look to see
where all the low voltage wires connect and make sure
none have come loose. The two wires running from that
terminal to the condensor in particular.
You also want to see if you have 24v at that point.