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Hi, We have a Carrier Transicold Zephyr 20S/30S Truck Refrigeration Unit. We are getting error message A02 which is a High Pressure cut-out warning. Question is what could be causing the error and how do we rectify the problem. Any help would be much appreciated.

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Posted on Jan 02, 2017

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SOURCE: I need an operation manual for a carrier transicold supra 644

You can order a manual at the following link;
Just select the Supra 644 through 844 series and I believe it is $6.99 to order from this site.

Posted on Oct 30, 2011

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SOURCE: need an operation manual for a transicold ultra xtc

We do not have this. Check with the manufacturer.

Posted on Feb 01, 2012

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Code a27 on carrier unit

AL27 A/D Accuracy Failure

The Controller has a built-in Analog to Digital (A-D) converter, used to convert
analog readings (i.e. temperature sensors, current sensors, etc.) to digital readings.
The Controller continuously performs calibration tests on the A-D converter.
If the A-D converter fails to calibrate for 30 consecutive seconds, this alarm is activated.This alarm will be inactivated as soon as the A-D converter calibrates.

Aug 07, 2018 | Carrier Heating & Cooling

1 Answer


I can find no A27 fault code for this unit, what is it doing? You can call carrier and ask for the definition, I think they will give it to you, just have the specific model number in hand when you contact them.

Aug 18, 2016 | Carrier Transicold Division Heat/cool...

1 Answer

I need to change the high pressure switch on my AC unit 2000 mercury sable how is this done

Since this a not the auto or truck area you might want to repost this there.

Aug 28, 2012 | Heating & Cooling

1 Answer

Need an operation manual for a transicold ultra xtc

We do not have this. Check with the manufacturer.

Feb 01, 2012 | Heating & Cooling

1 Answer

I need an operation manual for a carrier transicold supra 644

You can order a manual at the following link;
Just select the Supra 644 through 844 series and I believe it is $6.99 to order from this site.

Oct 29, 2011 | Heating & Cooling

1 Answer

Carrier unit pro earth ultra fresh II, unit stays on for about 15 min then everything shuts of, showing error: high head pressure

clean your condenser with air pressure to blow out the condenser or use spray bottle to wash down the condenser and fan blade wipe down and make sure all lint is removed from air flow passages!

Aug 28, 2011 | Carrier Refrigerators

1 Answer

AC Goes on and off in this excessive Heat.Must reset after rest.

The condenser coil is plugged and the unit is cutting out on high pressure....
Here is a tip that I wrote about how to clean your condenser

Cleaning Air ConditionerCondenser Coil with Pictures


Jul 23, 2011 | Carrier 38CKC042 Air Conditioner

1 Answer

We cleaned the coils outside. Now the compressor only stays on about 30 seconds and shuts off. It will come again in approximately 4 minutes. The fan outside and the blower inside stays on. We have a...

sounds like it's cycling on the high pressure cut-out switch. Note: it could be a low-pressure switch that is causing the cycling but most units (today) don't have low pressure switches. If your unit has either of these two switches it will (usually) be the high pressure switch, although it's possible it has the low pressure switch too. My guess is it only has a 'high pressure cut-out.'
I would seriously look at the coil again and make sure you've cleaned it real good.
Many Carrier Air Conditioners have what is called a SPLIT coil. If this is what you have you will need to (WITH ALL POWER OFF) disassemble the outside unit enough to where you can manually pull these coils apart (be careful - you just need to get a small gap between them) and wash IN BETWEEN the two coils.
Pretty difficult to do - but doable.
It's possible you have an overcharged unit - but unless you've recently had it charged I would not suspect this.
If it is not the high pressure switch - and 'you do have' a low pressure switch - chances are you're out of refrigerant and you will need a serviceperson to (a) fix the leak and (b) re-charge the unit

Jun 05, 2011 | Carrier 38BRC036 Air Conditioner

1 Answer

My outside unit runs, as does the inside; however, the air blowing from the registars is not cold. I replaced a component on the ouside unit a few years ago that solved the problem. it was located on the...

Hi, it sounds as though you had a problem with the disconnect box which is the only thing located on the exterior of the unit. You have to remove the cover to get to the wiring and fuses. Probably had bad fuses. In this case, the unit is up and running, so this wouldn't be the problem.It might be several things, like you may have a freon leak and lost some, or the condenser coil on the outdoor unit could be very dirty causing this not to cool. Try cutting off the power and taking your garden hose and washing the outdoor wrap around coil real good to remove any dirt build up. Careful not to use to much water pressure as you will flatten the aluminum fins. This might be your problem causing high head pressures. Do this and see if it does the trick.Make sure the fan is running and you can hear the compressor running also inside the unit. If its not running, you will have no cooling. Clean the coil and we can go from there. Get back to me and let me know the outcome, and we can go from there.
A/C, Heating, & Refrigeration

Aug 14, 2010 | Carrier 38CKC036 Air Conditioner

1 Answer



The High or Low Pressure sensors monitor the gas pressure on the system, ie: If your unit is low on gas due to a leak, or the system is building too much pressure due to an obstrucction, dirty condenser, or condenser fan motor fault, you'll be getting a message like the one you are getting now.

To find out what the problem is, have the unit serviced by an HVAC Technician.

Good Luck!

Aug 11, 2010 | Heating & Cooling

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