How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Phil Your Own Question
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 8768
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
Type Your HVAC Question Here...
Phil is online now
A new question is answered every 9 seconds

2006 carrier xtc, runs fine, cools good, all pressures good

This answer was rated:

2006 carrier xtc, runs fine, cools good, all pressures good but when it turns into defrost mode the discharge pressure spikes dramatically to 480 PSI and shuts off throwing out a high discharge pressure alarm.
JA: I'll do all I can to help. How long have you been dealing with this?
Customer: 2 days
JA: Do you plan on doing the work yourself?
Customer: I can
JA: Anything else we should know to help you best?
Customer: Sometimes I noticed that unit automatically turns into defrost mode and the pressure spike as usual but only get to about 442 450 PSI and then it turns into high RPM mode and the pressure drops to 250 psi within a second. Bad sensor? I just recently had it serviced and add refrigerant put in it as it was 11 lb low
JA: Did you double-check the thermostat? And what about the unit's filters?
Customer: Yes everything was checked and changed about 5 days ago


So far it looks like the system is over charged, 11 lbs is about twice as much refrigerant as most residential systems will hold...tell me what the name plate on the outside unit says about the refrigerant type (R410a most likely) and how many lbs or ounces it holds

Next I need the full and complete model number of the outside unit


Important note about RATING my work:

I am a retired mechanical engineer and HVAC/electrical/ refrigeration and boiler contractor... with 56 years in this business. The last 20 of those years consulting for major firms nationally..


All I ask is please respect me and my input by selecting the***RATING LINK***at the top of your page, that is the only way I am credited through the site.Rating does not affect your charges nor ability to refund if not satisfied.


If you need to be coached through a full diagnosis/repair,and wiring etc. for up to two days, and wish to be trained to use test instruments...... that goes well beyond' Just a simple Answer' of course, and goes beyond what most other experts here offer.....rate my simple answer so far positively.. and I will deliver that training and coaching to you All on the same dime so to speak.


Lacking a positive rating I can spend days helping a person at my own expense and loose my shirt,shorts and socks on the deal.


Attach a close up photo of the wiring diagram glued to the inside of the blower access door and I will mark it up with troubleshooting instructions then follow up with step by step training and coaching until you have a solution.


Photo must be exceedingly well focused. Use the 'add files' link next to your send button to get the photo to me.


Phone call offers:

If you wish to accept the companies $25 phone call offer,if indeed they send you one, this will go a *lot faster, but it IS 100% optional... or we can continue here in this dialog box at no additional charge.

Customer: replied 2 months ago.
This is a reefer unit on a 53foot trailer. My understanding was that they take 24 lb total of refrigerant. The refrigerant it takes is r404a

Thanks for the photo's.... remove 1 to no more than 4 lbs of the refrigerant until the red ball in the top sight glass of the receiver drops to the bottom of the top sight glass on the receiver.... then try it again, let me know how it goes.

Customer: replied 2 months ago.
Yeah I also notice to that. Usually the red ball would be somewhere in the middle or at the 30% but here it feels like there's so much freon that they don't even move around as if there's way too much pressure. How would I be able to remove that much without any equipment? Or at the very least where would I be able to get that equipment being on the road? I'm a truck driver currently passing Illinois going into Indiana on i80E. What type of a store should I look for? Or can I just open the charge line and slowly release the refrigerant until i see the red ball start to float in the middle? Or does it have to fall all the way to the bottom. I understand there's two sight glasses and you want the top Sight Glass ball to fall to the bottom but the bottom sight glass ball to stay floating at the top, correct?

Hello again, you want the top sight glass ball to just barely float, then remove 1 or 2 lbs of refrigerant. Refrigerant must be removed as a LIQUID, not in its gaseous form....

If you can find any service valves with hex head caps on them around that receiver take some photo's for me. Any commercial refrigeration tech will be able to remove that amount of refrigerant legally without having to know anything about that system. (listed under commercial refrigeration service in the phone book or google search, even most HVAC techs could do it, most would be afraid of the type of unit have however)

Best option would be a Carrier Transcold dealer or repair station. I will see if I can find one for you

click here for the transicold dealer map, you would be able find one easily in any area


Its time to rate my work so that the company pays me for my time, that will not close the question, we can go from there if needed

Customer: replied 2 months ago.
Are you saying that it is physically impossible to retrieve the refrigerant in a gas state? Or will it damage the system or let air in? Or are you just telling me that because it is illegal but possible? Since I have no way of getting to a dealer right now my question is what if I were to drain/ remove some refrigerant to the levels you're talking about and the unit will continue to have the same problem? What's the step two?
Customer: replied 2 months ago.
Also, I have absolutely no problem paying you for your knowledge, I just want to make sure we actually solve the issue

Refrigerant 404 and all of its cousins are *mixtures of several different refrigerants, if you remove as a gas you tend to get more of one of those gasses than the other... and that screws up the rest of the refrigerant left in the system... too much change and then performance goes crazy, something like putting a ltiny bit of gasoline in a diesel tank ... too many ounces would be a problem. when you remove refrigerant as a liquid, all of the various gasses come out evenly.

It would not be legal for you to let the refrigerant out of the system at the liquid line service valve, 1/4" service gauge connection with a small cap it over it, then turning the main valve stem on that same valve with a big cap over it. clockwise very slightly on that unit. There is a $25,000 fine for doing that.

The refrigerant also needs to be recovered to a waste refrigerant cylinder which you do not have, and that any licensed HVAC tech will have

click here please

Customer: replied 2 months ago.
Got it, I will definitely NOT do that. But in theory even dropping two or three pounds, which would be about 10 to 12% of the system, will really mess up the refrigerant inside? Also, what would be other symptoms that would indicate to us 100% that the system is over charged of refrigerant? I've gotten a lot of professional opinions but they all come back to this symptom ( cause and effect) being during normal operations, when I tell them it only happens when the unit goes into defrost, but otherwise it runs good ,they scratch their head and say oh, I'm not sure then. One thing is that I noticed it draws 10 amps when it goes into defrost, is that normal? Seems excessive no? Can it be a pressure sensor? Or is your professional opinion points everything to the system being overcharged. My main question here is, is there a possibility that something else is causing the unit to do this? Other than over charge of the system or are you 100% sure that that is the cause

when you remove refrigerant as a liquid, all of the various gasses come out evenly... so that will not mess up the refrigerant inside.

500 psig head pressure during defrost is the prime indicator of an over charge.

During defrost the extra liquid refrigerant is stored in the receiver with those two sight glasses. if there is no space in the receiver, liquid backs up into the condenser coil, and that runs up the head pressure.

10 amps is probably not an issue, I do not have the manual though so I cannot be more specific

pressure sensor will trip around 500 psig, a bad one would trip at too low a pressure... sensor is most likely good 95% chance of that, 5% chance its a problem.

A dirty condenser or evaporator coil will cause the system to run high head pressure under most conditions. those need to be kept clean and with their fans in good working order.

I am 100% sure that removing just 1 to 4 lbs of refrigerant will not hurt ... and 99% sure that it will solve the problem.

Customer: replied 2 months ago.
Understood. Yeah, that makes sense a lot of sense. I just had my Truck and Trailer Wash and I asked the guys to pressure wash the condenser on the reefer and there was so much dirt and crud that came out that they had to rewash the truck and trailer again. The fan is in good working condition and it's good airflow I'm sure. When you say keeping the coil clean what do you mean by coil? Where's the location of that coil?

The condenser IS a coil, the other coil is the evaporator that gets frosty when in cooling mode

My estimation of the over charge however is based on the top sight glass being full

Phil and other HVAC Specialists are ready to help you
Customer: replied 2 months ago.
Got it. Thank you very much for your time sir.

THat was tricky business, thanks for letting me know.