STRAIT A/C TROUBLESHOOTING HELP WANTED

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hvac tech12 in Concord, North Carolina

60 months ago

I have been working on a strait a/c system for a friend , they ask me to look at it since I have been in the field for a couple of years now. here is what I found. T he unit has not run in several years according to my friends. WHEN i STOP BY THE FIRST TIME ( 1-WEEK AGO)I turned the unit t- stat to fan on the blower started up so I knew the transformer was good ,I then turn the a/c on the compressor started up I put on my gauges , no pressure I cut the unit off and depressed the high side schader , very , very little pressure release. SO i get my jug of r-22 and charged system to 12 deg superheat and a s.p of 65 psi and a head pressure of around 200 psi outdoor temp around 86 or so. all ran good all week they complained the house was now to cold. 1 week later they call me and tell me its blowing hot air. im thinking loss of charge i had no way to leak search privously, when i return there i turn the tstat on copressor fires up i put my gauges on it reads 85 psi sp 182 head psi 30 deg super heat 7 deg subcooling 10.9 amps on compressor after 20 min. it cuts off. i figure the stat was satisfied for they had been running a window unit. SO I OPEN THE DOORS TO HEAT UP THE ROOM AFTER ROOM TEMP AROSE TO 78 I TURN STAT ALL THE WAY DOWN . this is a 95 unit and a very old t-stat (mannual not digital). compressor still will not start. I check low voltage across contactor coil, it was not pulled in and no power. i then checked wiring between yellow and common it read 26 volts . it has some kind of relay or it looks like a small control board with 2 diodes and 2 resistors on it an the leads from the contactor hook there, i checke voltage across it i had 26 volts. i could put a jumper on it across one leg of power from the contactor and common it would start up. i then removed the jumper it kept running, but my sp was still way high and my head psi was still a little low even after running 15 minutes low sub cooling and high super heat it acts like a valve in the compressor going

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hvac tech12 in Concord, North Carolina

60 months ago

hvac tech12 in Concord, North Carolina said: I ran out of space, it acts like compressor vaves going bad but my amp draw is still normal what are your thoughts anyone

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hvac tech12 in Concord, North Carolina

60 months ago

hvac tech12 in Concord, North Carolina said:
I had also cleanned the coils both of them so they were clean

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MIKE in Albany, New York

60 months ago

Call someone who knows what they are doing. HAHA

It sounds like you gotta look in the book. If I knew anything about this stuff I'd help but sry.

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andy in Phoenix, Arizona

60 months ago

there is alot of stuff that could be wrong. Zero is supposed to be read across red and yellow. Did you check the Low pressure, High pressure switch Its on the cooling line (yellow wire on the t-stat). you should read zero cause its a switch. It could be that you just undercharged thats the reason why you have low SC and high SH. The TXV is trying to maintain a constant super heat. I would take out the charge and recharge it by weight.( its on the nameplate). if it was the comp. valves your gauges would read high on the low side and low on the highside.
PS you could get fined up to $30,000 for the release of refrigerant into the air.

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coloradohvac in Parker, Colorado

60 months ago

hvac tech12 in Concord, North Carolina said: I have been working on a strait a/c system for a friend , they ask me to look at it since I have been in the field for a couple of years now. here is what I found. T he unit has not run in several years according to my friends. WHEN i STOP BY THE FIRST TIME ( 1-WEEK AGO)I turned the unit t- stat to fan on the blower started up so I knew the transformer was good ,I then turn the a/c on the compressor started up I put on my gauges , no pressure I cut the unit off and depressed the high side schader , very , very little pressure release. SO i get my jug of r-22 and charged system to 12 deg superheat and a s.p of 65 psi and a head pressure of around 200 psi outdoor temp around 86 or so. all ran good all week they complained the house was now to cold. 1 week later they call me and tell me its blowing hot air. im thinking loss of charge i had no way to leak search privously, when i return there i turn the tstat on copressor fires up i put my gauges on it reads 85 psi sp 182 head psi 30 deg super heat 7 deg subcooling 10.9 amps on compressor after 20 min. it cuts off. i figure the stat was satisfied for they had been running a window unit. SO I OPEN THE DOORS TO HEAT UP THE ROOM AFTER ROOM TEMP AROSE TO 78 I TURN STAT ALL THE WAY DOWN . this is a 95 unit and a very old t-stat (mannual not digital). compressor still will not start. I check low voltage across contactor coil, it was not pulled in and no power. i then checked wiring between yellow and common it read 26 volts . it has some kind of relay or it looks like a small control board with 2 diodes and 2 resistors on it an the leads from the contactor hook there, i checke voltage across it i had 26 volts. i could put a jumper on it across one leg of power from the contactor and common it would start up. i then removed the jumper it kept running, but my sp was still way high and my head psi was still a little low even after running 15 minutes low sub cooling and high sup

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coloradohvac in Parker, Colorado

60 months ago

First off have you checked if the filter is cloged. If the unit hasn't run for a while and was empty of refer there could have been corrosion or moisture in the lines that now has circulated and traped in the filter. When ever I encounter the same situaiton I like to replace the filter and pull a new vacume to make sure the lines are clean and DRY. Moisture in the system would explain the slight drop in pressure after refrigerant has cycled. Also like andy pointed out, make sure the TXV is working properly. Is the evap coil icing up at all? Excessive condensate is a tell tale after the unit has run for a while. As far as the power, determine if you have a 2 speed compressor. I've run accrossed units where the second speed won't come on but not the other way but not to say it can't happen, in that case you have a bad relay some where. Next time check for a leak beforehand by carging with nitrogen and I can't empasize this enough, pull a new vacume on units that are in ANY question of neglect or are empty of refer. Good Luck!

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robert s in Ada, Michigan

60 months ago

im in charlotte nc seeing how it has set for a few years i would pull all refrigerant out of the system then pump it up to about 350 psi of nitrogen get some bubbles and look for leaks if you cant find any visually then let it set for about 1/2 day if you lose pressure then find the leak but what im thinking is that you do have a leak and the system has gotten alot of moisture in it so let it pull a good vacuum maybe 2 days or so you may have to change your oil in your pump after the first day but see if you can get it down to at least 400 microns if it hold and doesnt lose at least 500 microns in 20 minutes then charge the unit by your superheat and you should be good to go i have about 14 yrs experience in res. and comm. hvac and comm. refrigeration so if anyone has any questions i would be glad to help out my email is uwantsumdis@hotmail.com

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John in Port Saint Lucie, Florida

58 months ago

Check your high voltage tap on your transformer and set it for the proper voltage. Replace the old t-stat,it's probubly causeing low voltage. Pull one wire off the contactor and test for volage between it and the terminal it came off of.
It sounds like you have a time delay relay for the compressor.You can bypass it and get rid of it but I suggest getting a stat that has one built into itself. What type of unit and compressor. is it a split system, Pack, or what.

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Tony in Buffalo, New York

56 months ago

[Sounds like the thing with the diodes is a time delay relay that either is timing out or faulty) This willl prevent short cycling of the compressor especially with a non digital thermostat.

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Collin in Spring Hill, Florida

55 months ago

All of the suggestions are partially correct. You have multiple problems most definetly a leak in sys. With high back pressure a week after charge and high s.h. low s.c. I would check your ducts especially return to make sure its not pulling hot air from attic directly into evap. Most important reclaim charge. Nitro flush system fix leak. change filter drier add drier to suction side also put on long vacuum.

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athompson in Omaha, Nebraska

55 months ago

Collin in Spring Hill, Florida said: All of the suggestions are partially correct. You have multiple problems most definetly a leak in sys. With high back pressure a week after charge and high s.h. low s.c. I would check your ducts especially return to make sure its not pulling hot air from attic directly into evap. Most important reclaim charge. Nitro flush system fix leak. change filter drier add drier to suction side also put on long vacuum.

wanna work for a great company? chance in a lifr time?

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Hvac Pro in Las Vegas, Nevada

55 months ago

Here's my approach.

FIX THE LEAK , first.

of course r/r the filter driers or add them.

then Vacuum at least 45 minutes minimum with a micron gauge.

then weigh in the charge, and top it off if needed.

Next, take a delta -t and monitor your gauges , they will tell you everything that is going on.
learn how to read them and what they mean.
;) nine times out of ten there will be a combination of problems, usually a chain reaction....

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danny ray in Birmingham, Alabama

54 months ago

hvac tech12 in Concord, North Carolina said: I have been working on a strait a/c system for a friend , they ask me to look at it since I have been in the field for a couple of years now. here is what I found. T he unit has not run in several years according to my friends. WHEN i STOP BY THE FIRST TIME ( 1-WEEK AGO)I turned the unit t- stat to fan on the blower started up so I knew the transformer was good ,I then turn the a/c on the compressor started up I put on my gauges , no pressure I cut the unit off and depressed the high side schader , very , very little pressure release. SO i get my jug of r-22 and charged system to 12 deg superheat and a s.p of 65 psi and a head pressure of around 200 psi outdoor temp around 86 or so. all ran good all week they complained the house was now to cold. 1 week later they call me and tell me its blowing hot air. im thinking loss of charge i had no way to leak search privously, when i return there i turn the tstat on copressor fires up i put my gauges on it reads 85 psi sp 182 head psi 30 deg super heat 7 deg subcooling 10.9 amps on compressor after 20 min. it cuts off. i figure the stat was satisfied for they had been running a window unit. SO I OPEN THE DOORS TO HEAT UP THE ROOM AFTER ROOM TEMP AROSE TO 78 I TURN STAT ALL THE WAY DOWN . this is a 95 unit and a very old t-stat (mannual not digital). compressor still will not start. I check low voltage across contactor coil, it was not pulled in and no power. i then checked wiring between yellow and common it read 26 volts . it has some kind of relay or it looks like a small control board with 2 diodes and 2 resistors on it an the leads from the contactor hook there, i checke voltage across it i had 26 volts. i could put a jumper on it across one leg of power from the contactor and common it would start up. i then removed the jumper it kept running, but my sp was still way high and my head psi was still a little low even after running 15 minutes low sub cooling and high sup

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danny ray in Birmingham, Alabama

54 months ago

hi have you checked the inside filter its sounds like dirty outdoore unit or stoped up evap coil in thr inside

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danny ray in Birmingham, Alabama

54 months ago

air flow problems if the outside is restreted it cause high suc and low head

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Hvac Pro in Las Vegas, Nevada

54 months ago

this thread is like stepping in a bag of dung on fire. lol

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sualways@yahoo.com in Dubai, United Arab Emirates

53 months ago

hvac tech

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geo in Elizabeth, Pennsylvania

53 months ago

Sounds like you have non condensables in the systems. reclaim refrigerant. pressure test systems with nitrogen 250psi. you will hear a leak at that pressure. fix leak. change or install filterdryer. vacume down to 400microns. and recharge the unit to how many lbs it calls for on the name plate. Yeah i know it sucks but i'm positive that should fix it. also check that fan speed is on hi in cooling. change air filter

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bogle67@hotmail.com in Normangee, Texas

51 months ago

hvac tech12 in Concord, North Carolina said: I have been working on a strait a/c system for a friend , they ask me to look at it since I have been in the field for a couple of years now. here is what I found. T he unit has not run in several years according to my friends. WHEN i STOP BY THE FIRST TIME ( 1-WEEK AGO)I turned the unit t- stat to fan on the blower started up so I knew the transformer was good ,I then turn the a/c on the compressor started up I put on my gauges , no pressure I cut the unit off and depressed the high side schader , very , very little pressure release. SO i get my jug of r-22 and charged system to 12 deg superheat and a s.p of 65 psi and a head pressure of around 200 psi outdoor temp around 86 or so. all ran good all week they complained the house was now to cold. 1 week later they call me and tell me its blowing hot air. im thinking loss of charge i had no way to leak search privously, when i return there i turn the tstat on copressor fires up i put my gauges on it reads 85 psi sp 182 head psi 30 deg super heat 7 deg subcooling 10.9 amps on compressor after 20 min. it cuts off. i figure the stat was satisfied for they had been running a window unit. SO I OPEN THE DOORS TO HEAT UP THE ROOM AFTER ROOM TEMP AROSE TO 78 I TURN STAT ALL THE WAY DOWN . this is a 95 unit and a very old t-stat (mannual not digital). compressor still will not start. I check low voltage across contactor coil, it was not pulled in and no power. i then checked wiring between yellow and common it read 26 volts . it has some kind of relay or it looks like a small control board with 2 diodes and 2 resistors on it an the leads from the contactor hook there, i checke voltage across it i had 26 volts. i could put a jumper on it across one leg of power from the contactor and common it would start up. i then removed the jumper it kept running, but my sp was still way high and my head psi was still a little low even after running 15 minutes low sub cooling and high s

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mrchill_68 in Shreveport, Louisiana

51 months ago

First of all,how old is your unit? It may not be worth your time and money to make the repairs.It sounds like you have a bad valve in your compressor allowing discharge gas to escape back to the suction side.This will cause you to have a high superheat.Remember your evaporator coil must be compatible with the industry's new condensors.It would be feasible to change out the evaporator coil as well.By the way noncondensibles will cause both high discharge and suction pressures.

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mrchill_68 in Shreveport, Louisiana

51 months ago

change out the condensor the evaporator .

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mrchill_68 in Shreveport, Louisiana

51 months ago

a dirty evaporator or dirty filters will cause you to have a low suction pressure.A dirty condensor will cause you to have a high discharge pressure.If your refrigerant charge is low and you have a low pressure switch it will lockout your low voltage to your compressor contactor.If you bypass this switch the compressor will start.Once it builds up enough pressure from running,it will continue to run.

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gil in Ansonia, Connecticut

50 months ago

the system has leaked the gas out. At that time it may have sucked in air if it was leaking on the low side even if pressure was still in it the low side can go below atmosphere and pull air in you should always pull system down with vacuume pump after recovering any refrigerant left the drier should be replaced beforehand as well and the leak located and fixed. as far as the pressures go it does sound like the compressor is not pumping properly and needs replacement thay get hot and shut down do to the high superheat resulting from its reduced pumping capacity make sure it does not have a suction line filter if it does it could be pluged if you replace the the compressor check oil for acid with litmis paper use a charcoal drier.it is necessary to leak test the system with nitrogen and spend time on evaporator.it can be hard to find cover with saran wrap and make hole through it for leak tester.if you cant find the leak prob do for new sys.

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Stan in Chattanooga, Tennessee

47 months ago

I have read some of the comments here some suggestions are good first question would be have you fixed the problem by now . Time delay is right for your control your head pressure is low suction pressure is high no temps what is discharge temp and what is suction line temp. them wet bulb and dry bulbs inside return and supply lines . and the suggestion about no refrigerant in lines and has been dead awhile always remove old drier add new liquid line drier and even suction line drier to pull trash out. pull good long vaccum. if you have micron gauge use it do a triple vaccum and purge with nitrogen. Didn't say if you have a piston system or expansion valve system. if is 95 yr propably old 10 seer with pistion. Everything depends on superheat from there need good temp. if you have done all this and system still not operating correctly well lets just say feedback helps and go from there

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John Marcantonio in Winter Park, Florida

46 months ago

I have been doing commercial a/c and refrigeration for 22 years. If unit has not run for 2 years and lost its charge, check core valves, they leak.If not then leak check with leak detector. If you can not fine leak then reclaim unit and use nitrogen to find leak. If not in Evap. or condensing unit,disconnect line sets after removing nitrogen, seal each end of line sets with port valve. put nitrogen in line sets and hook up single high pressure gauge to port valve. do this for both suction and liquid line. If one leaks change both out if under ground, if you can get to lines cut area of leak, sweg line, solder, connect lines back up,purge with nitrogen,vacuum and charge. If you had to jump out curcuit board timer is bad in board. As of pressures I have seen units run low suction do to blockage in duct work or pluged filter that was never taken out from factory filter area at air handler. orfice could be restricted at air handler, pulged drier, pin hole leak in drier around ends where driers were factory welds. 200 PSI is not uncommon on some units due to load factors. Here in Florida during winter time which is not very cold but little humidity, we have to put a fan cycle contol on them,factorys dont,but read there paper work or on eletrical diagram it will so it as a option. Some times condensing unit gets chaged out and air handler does not. This can also be a problem with pressures. Good luck......

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Juiceman in Baton Rouge, Louisiana

46 months ago

all responses were helpful

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sam in Odenville, Alabama

44 months ago

hvac tech12 in Concord, North Carolina said:

if it has a txv it might be bad or out of adjustment

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sam in Odenville, Alabama

44 months ago

hvac tech12 in Concord, North Carolina said:

if it has a txv it might be bad or out of adjustment

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Acpro in Buffalo, New York

20 months ago

Actually were looking for US citizens who speak, read and write English well. We would like to employ an out of work citizen over a outsider. Work on your Enlish. I'd say no - we would not employ you.

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