Odd fan/compressor sequence?

[Carry On]

Carrier 5T Heatpump system with a Focus Pro 5000 thermostat.

While the AC was operating, I raised the temperature 2 degrees. A few minutes the AH fan shut down (after the normal delay), but the compressor kept running, would not turn off even if I took the T-stat out of cool mode. I pulled the outside breaker, turning off the compressor. Now the system works normally: temperature reached, compressor shuts down, a few minutes later the AH fan shuts off.

What could have caused the compressor to keep going with the AH fan off?

Could changing the temperature setting on the T-stat have temporarily scrambled something in the T-stat that could have caused this.

But I thought the AH fan was turned on and off from a contactor at the condensor that also controls the compressor/fan contactor preventing the compressor from operating without sending power to the AH.

What would have happened if this had happened if I did not pull the breaker?

Thanks for help.

[beenthere]

The OD unit doesn't any control over the indoor unit unless its 2 stage.

Your stat may be wired or configured wrong.

If its a new install, call your contractor back.

[Carry On]

It's not a new install. The system has been working fine this winter in HP mode and this summer in cool. The manual fan control works too.

It seemed like the stat hung up. Has that happened with this type if the temperature is changed too quickly under certain circumstances?

The system operating normally now. I am not sure I could duplicate what happened but something did.

When would the condensor have kicked off and what condition would have caused it? I suppose that the coil would have frosted up, but without air running over it not much ice would have accumulated before the condensor shut itself off.

[Shophound]

Hard to say for certain what exactly caused your problem. It's possible the triac or relay inside the thermostat that energizes/de-energizes the compressor contactor got stuck on. Also possible the compressor contactor itself got stuck on. When you hit the breaker, the contacts cooled enough to let go...possibly. If the system has a few years on it and you've never had the outdoor compressor contactor replaced, might be a good idea to get that done. Being it's a heat pump, the compressor runs year round, so contactor life is used up more quickly than for straight a/c.

[Carry On]

New contactor and fan on the condensing unit in January.

Damdest thing.

As said before, what would have happened if I was not around, although I suppose if I wasn't the temperature setting would not have been manually raised is some way that caused the odd operation.

I thought that as long as the compressor contactor was closed, the AH fan would run. It's a SP fan, but runs for about two minutes after the compressor stops. I thought the control for that was in the condensor.

[beenthere]

Its not.

[justinj1635]

problem with the stat, if it was wired wrong you would have noticed by now.

those focuspro stats are pieces of ****, changed a few this year already due to failure..and they were less then 2 months old.

[beenthere]

haven't had a problem with them. What were they doing or not doing.

[justinj1635]

i had 2 that decides to "pop out" of there designated equipment mode.

these have the ability to run 1/2/hp/oil fired/etc type equipment. and you set it for whatever your running, but i had 2 different customers, with completely diff equip, one was a 2 stage rtu, so it was set for 2 stage on the stat. got a call back it was hot, so went back, the stat had set itself to only 1stage system, and wouldnt come out of econo when it was hot. did this 2 or 3 times and just said f-it. changed the stat. same thing happened about a month later at a different customer.


i never liked the green color anyway

[beenthere]

Ok, 2 out of how many?

[cmajerus]

New contactor and fan on the condensing unit in January.

Damdest thing.

As said before, what would have happened if I was not around, although I suppose if I wasn't the temperature setting would not have been manually raised is some way that caused the odd operation.

I thought that as long as the compressor contactor was closed, the AH fan would run. It's a SP fan, but runs for about two minutes after the compressor stops. I thought the control for that was in the condenser.

give the service guy a call, your outdoor equipment needs attention. The stat is not going to keep the condenser on without the air handler on.

[Carry On]

Would the compressor have shut down automatically without the AH operating?

[beenthere]

Depending what model outdoor unit you have, it should have a safety switch that wouold have cycled it if the pressure got too low. Not sure if it would lock it out though.

[Carry On]

How much ice would form on the evaporator without the AH running? I suspect that when the thermostat again called for heat within 20 minutes, the condensing unit and AH would have synchronized. It's working fine. Electronics?

[beenthere]

If it doesn't have a safety, a lot of ice, if it has a safety, a fair amount.

I'd have it checked. You don't want it to go the opposite direction, and not run at all.

[Carry On]

The system continues to cycle normally. I doubt that a technician could find anything unless I can repeat problem. I guess it's possible that the condensor contactor hung up, but odd that it only happened once and only when I raised the t-stat a few degrees, which I will try again to see if it happens again. If it does then the problem would have to be in the t-stat, which be very odd. I thought that it was impossible for the compressor run without turning on the AH fan and that the delayed fan shutdown was controlled from a board on the condensor unit. Of its there a board for that in the air handler.

You would think that if the thermostat hung up, it would keep both the AH fan and compressor on? Unless it controls the AH fan sepearately, meaning the fan shutdown board is in the air handler.

The circuits that I have seen in general seem so show that a T-stat controls a contactor that turns on both the compressor contactor and a contactor for the fan control. Since the fan shutdown normally and the compressor did not, that contactor worked and the compressor contactor stuck, it would seem. But what could be the connection to raising the T-stat temperature. That's what puzzles me. Unless the t-stat controls the fan and compressor separately and it was temporarily scambled so that it turned off the fan but not the compressor.

[beenthere]

They are controlled seperately.
Other wise, if you turned your fan to on, the compressor would run.

[Shophound]

If the FocusPro is similar to the VisionPro, it has two triacs/relays, one for cycling the compressor and the other for the indoor blower. The VisionPro makes a distinctive "click-click" when activating both compressor and indoor blower, and the same for when they are de-energized, unless the thermostat itself is programmed to perform the blower off-delay. You'd then hear just one "click", followed a minute or so later by the other "click".

So, listen to your thermostat when it calls for cooling...does it go "click-click"? Same for when it is satisfied and is switching off the equipment? If you want to repeat the increase in temperature scenario which coincided with the problem stated in the OP, listen to the thermostat when you do. If it normally goes "click-click" when shutting the system down, but you now hear only one "click", and the compressor is still running, but the blower stops, the thermostat relay for the compressor could be hanging up. I notice at times my VisionPro "click-click" seems a bit more spread out than usual, but it's the second "click" that is delayed, which is for the indoor blower. The compressor always shuts off on the first "click".

Worst thing that can happen with indoor blower shutting off but compressor continuing to run is the evap coil ices up, which at best only means no airflow, at worst could mean water damage to the structure and/or damaged compressor.