Air Conditioning problem
2001 Isuzu NPR 4 cyl Two Wheel Drive Automatic 249243 miles
Having some problems with this customer's A/C and wanted someone's input. I replaced the condenser fan and system dryer using OEM parts in May. A/C was working fine the past two weeks until the outside temps started climbing; I'm in North Charleston, SC and have had temps in the 90's & near 100 the past couple weeks. I have the system charged to good low/high side pressures (no sight glass) and with approximately 44 deg. Vent temp at 2000 rpm. Twice in the past two weeks the driver has been on a hour and a half round trip and on the return leg the dryer has blown off pressure from the system and it loses r134a and coolness. I charged it back up the first time and checked and didn't see any problems. The second time I charged it it was showing the high side reading up around 250 psi so I didn't charge it any more. Two days later the driver told me the same thing had happened again, in the same way and on the same route; it never happens on any other route. I checked the system yesterday and recharged with approx. 1/2 lb. Of 134a. At idle the compressor engaged readings were 23 psi low/165 psi high & compressor disengaged readings of 40 psi low/165 psi high. At 2000 rpm the comp engaged readings were 20 psi low/210 psi high & comp disengaged readings 40 psi low/165 psi high. The compressor cycle time at idle was approx. 15 seconds engaged/10 sec disengaged; the cycle time at 2000 rpm was 20-25 sec engaged/10-15 sec disengaged. I was thinking earlier that I had a high side restriction somewhere that was causing the HS pressures to spike under certain conditions but the readings I got yesterday don't indicate that. Would like to know the system operating pressures for this vehicle and get any suggestions you may have; dealer hasn't been very helpful with this.
Does condensor fan go into high speed mode? Is there a pressure switch on receiver/drier?
Let me know
Thanks for donate
June, 25, 2009 AT 4:37 AM
To my knowledge the cond. Fan only has one speed and I think it comes on around 150-170 psi high side; can't remember the pressures for certain. There is a pressure switch on the drier; the original OEM drier also had a sight glass but the replacement OEM drier I installed doesn't. The sister truck to this one has a sight glass in-line just before the high side connector port.
June, 25, 2009 AT 4:49 PM
Condensor fan has two speeds check relays one for low speed and another for high. If no high when head pressure goes upit can't cool. Also check pressure switch it is dual for low and high it should cut out long before drier blows.
Refergient full charge is 22.9oz
June, 26, 2009 AT 3:31 AM
Thanks, didn't know about the two speeds. Do you have anything that shows what the pressures should be? I won't see the truck till next week but will definitely check this and would like a comparison on the pressures.
June, 26, 2009 AT 1:41 PM
Need to know 2.2L or 3.2L?
Operating pressure range High side 199-270 Low side 21-43 psi at 77-86 deg. Air temp