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Old 06-26-2011, 07:16 PM   #1
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Old carrier unit trouble


Have a really old Carrier 3.5 ton unit which has served me well for a long time, in fact all I ever did was replace a bad fan motor and contactor years ago.

My problem is that with the recent heat here in Texas (105-113) the unit does not cool well nor will it shut off when it gets over 100. Late in the evening until next afternoon it does just fine, in fact gets so cold in the house I have to turn the thermostat way up. Ran a check this morning at 10AM with an outside temperature of 88 and humidity of 55; suction line had a pressure of 69 and a temperature 40, temperature at indoor vent was 50. Kept my gauge on there for about 45 minutes, stayed the same. Ran the ac with it cycling just fine until mid afternoon with an outside temperature of 105 when it reverted to doing what it has been for over a week, temperature at register 70-75, suction line barely cool and never shutting off. Tried a few times turning the unit off for about 20 minutes and back on but to no avail. Just a little while I tried again and this time it worked, register temperature is at 60 which is normal late in the afternoon as I have a southern exposure and the house will warm up quite a bit that time of day and itís still 108 outside. By late in the evening the register will be again at 50-55 and suction line ice cold. I should add that I also ďrattleĒ the thermostat from one end to the other while trying to get the unit to cool back down; whether that really helps, I donít know. I also took a look in the control box and all looks good, no burned wires, run capacitor is not bulged or damaged. Also cleaned the coils on the unit. Did not take a high side reading, maybe tomorrow.

Something is keeping the unit from cooling properly in the afternoon. Right now, early evening itís doing just fine. Itís like something gets stuck and then corrects itself after a few tries of shutting down, restarting and playing with the thermostat. Could a weak run capacitor cause my scenario? I donít have a tester but found replacement capacitor on the internet. Sorry to be so long winded, any help short of telling me to buy a new unit is appreciated.
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Old 06-26-2011, 07:53 PM   #2
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Old carrier unit trouble


the sun swing and the heat rise on the day is driving the condenser and compressor and the pressures rise accordingly with the inlet air.10F rise on air in and air out is typical on most condensers with 18F slit on the air handler air supply/return...shut the condenser power remove the access panel and hose the coil easy on the nozzle pressure.if you R-22 freon the days temps should run 30F above the inlet air temp on the condenser....the inside temp ring on the hi side guage for r-22 f your over that temp example...inlet 80F +30F +110F check needle position for 110F then pressure will be right above it on the outer pressure numbers.the liquid line should be warm but never hot only on the high of the day if it is hot at 80F then your condenser is resticted wash it out...good luck http://www.youtube.com/watch?v=J7oPhjknZdQ
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Last edited by biggles; 06-26-2011 at 07:59 PM.
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Old 06-26-2011, 08:05 PM   #3
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Old carrier unit trouble


Hosed down the condenser coils several days ago; evaporator coils about 3 years ago (hard to get to).
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Old 06-26-2011, 08:43 PM   #4
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Old carrier unit trouble


For a while I thought that the unit not shutting itself off and restart might have something to do with the problem but once I get it going again I can let it run all night, cooling the house down to 70 until I shut it off at the thermostat. As it is doing right now with the outside temperature still at 105! Like I said, something puts the unit into the trouble mode until I can restore it back to normal by shutting it off for a while and then turn it back on and/or playing with the thermostat.

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Old 06-27-2011, 09:37 AM   #5
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Old carrier unit trouble


the pressure within the system might be rising to a point where it trips the hi pressure switch which might need the manual shut down start up....how long do you wait before turning the outside disconnect back on?the outside temps and the sun banging the condenser are the problem..if it was a capacitor problem or electrical it wouldn't run during the cooler nights...piping sound tight with the original charge still there...good hsing out of the condenser might be the fix.....how does the liquid line feel coming out of the condenser..in the PM and in mid day average is warm at 80F compressor running..if it is maint. the night it has to be cycling and restarting as normal....do you have a digital stat with a compressor off time which allows the pressures to equalize before the next start. i want to hear back on my inquires before telling you to add something..how often do you put guages on the unit..the hi side guage reading is more important for me to see what the pressure is running vs the inlet days temp...your house system reacts the same your car ac acts in the hot weather normal running pressures say in your nights 65PSI=40F at the air handler coil...250PSI with 75F-80F air into the condenser..if the outside changes with the days temps the hi side changes rising up,and that pushes the suction pressure up 70psi-80psi and there goes the temp at the air handler 40F...55F...65F supply
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Last edited by biggles; 06-27-2011 at 10:00 AM.
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Old 06-27-2011, 12:37 PM   #6
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Old carrier unit trouble


Itís noon here with 91 degrees and 43% humidity. Unit was running fine all night cycling on and off with no problem. This morning it was again 50 degrees at the register and currently is still running ok, the high pressure line is warm, not hot and the suction line is nice cold and wet. Still have not taken a high pressure reading but with the way its running since 5:30PM yesterday I figure itís got to be ok. Of course that may change in 2 or 3 hours if and when it goes into ďtrouble modeĒ. When that happens the unit keeps running, never shuts off, suction line feels barely cool high pressure line feels hot and temp at the register is about 70-75; Iím totally perplexed as to really what brings it back on after several tries of turning it off for about 20-30 minutes, then back on and moving the thermostat dial from one end to the other. If thermostat were bad I would not get the cold temperatures Iím getting once I have it going again late in the day, no? One little item I need to add here. I asked about the run capacitor on my sonís recommendation. I was out oftown and just this morning my son tells me that while I was gone a 6Ē-8Ē wire between the run capacitor and the contactor had fried completely, one end to the other and he replaced it with 8 gauge piece of wire whichgot the unit going again. So it seems all of this started when that wire burned; I didnít know about this yesterday when I posted. Took the covers off this morning as I did yesterday, everything in the control box looks clean, the contactor looks like new, no other burnt wires and the run capacitor is clean with no bulges No digital stat and I hosed the condenser coils twice. As of now the unit still runs cold, temp at the vent is still below 60 but today I got the thermostat set really low (71). Weíll see what happens in the next few hours and Iíll post. Iím not a pro by any means and most of what I know about HVAC Iíve read; am trying to avoid calling a technician, too expensive and in this town they all want to sell you something rather than work on something as old as this unit which really has been relatively trouble free; certainly no problems like Iím having now. Iím just an old geezer trying to survive on SS.
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Old 06-27-2011, 02:50 PM   #7
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Old carrier unit trouble


ok so withthe cap and contactor wires cooking thats telling me the compressor is trying to start on a short cycle and not having enough time to equalize from the last cycle the pressures run as i said 260psi + hi and 65psi suction cold line....when the unit cycles offf from the stat it needs to balance those pressures before the next cycle if they dont and the stat calls the compressor will never start and draw very high amps(burnt wires as found) might consider adding a time delay relay http://www.bestbuyheatingandaircondi..._Code=REL203AA in the condenser in line with one of the 24v control wires from the stat coming in.do you have ant electronic boards either in the condenser or air handler??? the resetting of the stat to get it to run is sounds like something is locking your condenser and waiting on a 24V reset when you work it.have your son check the compressor contact see if its arc'd on the contacts might need changing with the compressor trying to restart against that un equalized pressures...i'll check back...NOTE if you go to start it right after it goes off you will not get the compressor to run only do it 15minutes after the first time it trips off...keep note on that Liquid Line as it gets hot as the day temps rise...it may look clean but the coil might be blocked between the coils ...the heat rise on the LL with the days temp rise willl tell me that...
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Old 06-27-2011, 05:11 PM   #8
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Old carrier unit trouble


Well, as expected it did it again. About 3:15PM, 106 outside, 10% humidity, suction line cool but not cold, high line much warmer as was this morning when all was well and uncomfortable to the touch, air at register about 73 with the house warming up fast. Shut it off and waited 30 minutes, turned it back on - no improvement, watched it for 10 minutes - no change. Here comes the kicker! Went to the thermostat and sharply turned the dial from one end to the other 3 or 4 times and immediately it kicked in, air temp at the register dropped almost immediately and is now back at 60 with the suction line back to normal but the high side still uncomfortable to the touch. Is it just my imagination or could it be caused by the thermostat after all (weak voltage)? No electronic boards on this unit! Only circuit board I know of is on the inside of the house at the furnace. I'm almost embarrassed to do this but the Carrier model # of this unit is a 38GS045300 which makes it almost 40! Same goes for the furnace. As I have already stated, I never have had any major problems other than what was caused by power surges because the city had me hooked up 400 yards away, after an apartment complex and multiple duplexes I was the last on the grid. I used to mysteriously lose TV's, VCR's, Coffee Makers and Micro Waves too. It all changed back to normal when we had one really strong thunderstorm one night and the AC was going haywire, surging up and down, making a racket. When the guy from the power company showed up he was aghast at how far away they connected me when I had a pole right in back of my house. He made the switch and that took care of that problem. Anyway, could it be the thermostat? Whatever needs to get done will have to be by me and/or technician. My son was just house watching and knows less than I do; smart enough though to check the control box and find the burnt wire. AC is still working fine at 5:05PM.
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Old 06-27-2011, 06:15 PM   #9
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Old carrier unit trouble


On second thought I donít think itís the thermostat; works fine all night and the better part of the day, cycling in and out as it should. My problem happens only in extreme heat when the compressor has been cycling four hours just fine but when the temp goes way up it wonít kick back in until I do my thing. Just funny though how the unit responded immediately this afternoon when I played with the thermostat. Found wiring diagrams for the unit on the internet. Unit is still running fine, I have not let it cycle though just in case it does not want to kick back in; itís 106 outside.
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Old 06-27-2011, 06:55 PM   #10
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Old carrier unit trouble


from either over amps or high head lock out thats why it restarts after resetting the stat which on the 24v circuit resets the condenser being locked out...the unit safty(s)are reacting to the rise of the day...need to get a service guy in..can you put up the schematic
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Old 06-27-2011, 07:25 PM   #11
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Old carrier unit trouble


http://www.xpedio.carrier.com/idc/gr...t/38gs-1si.pdf

http://www.xpedio.carrier.com/idc/gr...it/38gs-1w.pdf

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Old 06-27-2011, 07:31 PM   #12
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Old carrier unit trouble


Sorry about that! Posted a wrong link on first reply. My model 38GS045300.
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Old 06-27-2011, 08:57 PM   #13
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Old carrier unit trouble


that CPCS has one of the compressor line wires going thru a CT sensing the current when the compressor is running any extremes in currant and the unit locks out..higher temps will cause higher amp loads...hows the power suppliers there if they brown out on the incoming volts the amps might rise and trip along with the hotter temps...any idea on the actual voltage readings when the compressor is running..might have to change the comp protection board or eleminate it to stop the trips
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Old 06-27-2011, 10:17 PM   #14
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Old carrier unit trouble


Looks like you said, time to bring in a technician. Hope I can find a capable and honest one! Set the thermostat to where itíll cycle off and on about 8:00PM when it was still 100 degrees and itís been working fine. Itíll be nice cold crisp by early AM until the next go around. Just to understand in plain language, the high heat in the afternoons is causing the pressure to rise on the high side and/or sending incorrect voltage to the compressor? Please correct me on this if Iím wrong. Still donít understand what caused this all of sudden.
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Old 06-28-2011, 06:19 PM   #15
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Old carrier unit trouble


The unit has been running fine since yesterday afternoon, cycling off and on as it should during the nightand better part of today until it got hot when it just kept running but keeping the house cool. About 5:30PM after running like that with an outside temperature of 99 I decided to try testing it again. I shut it off with the off switch on the thermostat, waited 15 minutes and turned it back on with the cool setting on the thermostat; no rapid turning of the temperature dial on the thermostat this time. Unit turned back on like it should, compressor kicked in, house is cool. Perhaps the outside temperature was not enough to allow the unit to slip into its trouble mode?
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