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Car Forum / Volvo Cars / October 2005AC Problem - lines froze
Situation where if AC on low fan, both the high pressure and low pressure lines froze - frost on both lines. Pretty soon, blowing warm air only. Fan on high, not a problem. Also compressor seemed to fail to cycle, running all the time, and gas mileage dropped badly. How do Volvo's control the clutch and cycling of the compressor? Thanks my guess is that you are low on coolant .... R12 in older systems, R134a in newer ones... > Situation where if AC on low fan, both the high pressure and low > pressure lines froze - frost on both lines. Pretty soon, blowing warm [quoted text clipped - 6 lines] > > Thanks We really need to know model/year on this, and if the year is earlier than about 93 whether the system has been converted to R134a. Something that strikes me is "frost on the high pressure line." Is this the line from the condensor, past the valve, where it enters the evaporator? (If not, I'm lost.) Mike > > Situation where if AC on low fan, both the high pressure and low > > pressure lines froze - frost on both lines. Pretty soon, blowing warm [quoted text clipped - 14 lines] > > Mike High pressure line = liquid line = the line from the compressor to the orifice tube or expansion valve. >> > Situation where if AC on low fan, both the high pressure and low >> > pressure lines froze - frost on both lines. Pretty soon, blowing warm [quoted text clipped - 19 lines] > High pressure line = liquid line = the line from the compressor to the > orifice tube or expansion valve. That's what doesn't figure. That part should be hot under all conditions (except compressor off). The section from the valve to the evaporator can be cooled to frost by flash gas if the system is running full bore. To that extent, I think the OP was doing the best by focusing on why the compressor was always engaged. Mike > > High pressure line = liquid line = the line from the compressor to the > > orifice tube or expansion valve. [quoted text clipped - 6 lines] > > Mike If there is frost on the liquid line and the system has the proper charge then there is a restriction in the line just prior to where the frost starts that acts like an expansion valve. If it is a model that has the orfice tube under the hood it's possible for the high side line to frost when the system charge is low. Bob  SignatureThe goal when driving is to miss the maximum number of objects. > >> > Situation where if AC on low fan, both the high pressure and low > >> > pressure lines froze - frost on both lines. Pretty soon, blowing warm [quoted text clipped - 27 lines] > > Mike Er, I forgot to mention the condenser in there, the line goes from the compressor to the condenser, and then to the expansion device. The line between the condenser and expansion device shouldn't be hot, but it should be a bit warmer than ambient depending on condenser efficiency. If that line is iced up it can be one of two things, a kink or blockage causing a pressure drop and some of the refrigerant to boil off in the line rather than in the evaporator, or the evaporator can be so iced up that the liquid line ices up nearby just from conduction. 1998 S70 - so it's the new stuff plenty of freon though ~40# per mechanic actually, the high and low pressure lines were freezing as they exited and entered the firewall. think it may be fixed now, replacing the high pressure switch and expansion valve seems to have done the trick > 1998 S70 - so it's the new stuff > plenty of freon though ~40# per mechanic [quoted text clipped - 4 lines] > think it may be fixed now, replacing the high pressure switch and > expansion valve seems to have done the trick 40 pounds?! That can't be right, the system only holds about 2.5 pounds. If that's the pressure he's referring to it sounds far too low for the high side and too high for the low side. If the expansion valve is stuck open it can indeed cause the evaporator to completely freeze up which will also ice the lines going through the firewall. The valve's purpose is to regulate the flow of liquid refrigerant into the evaporator by monitoring the temperature of the suction line, you want just enough so that it boils almost completely away using the entire surface area of the evaporator but still leaves just enough liquid refrigerant to cool the compressor. >>1998 S70 - so it's the new stuff >>plenty of freon though ~40# per mechanic [quoted text clipped - 6 lines] > > 40 pounds?! That can't be right, the system only holds about 2.5 pounds. If 40 psi? That's too high, IIRC about 20-25 psi is a normal reading on the low pressure side (where you add freon) while the system is running. > > 1998 S70 - so it's the new stuff > > plenty of freon though ~40# per mechanic [quoted text clipped - 16 lines] > surface area of the evaporator but still leaves just enough liquid > refrigerant to cool the compressor. 2.5*16=40 oz. Bob SignatureThe goal when driving is to miss the maximum number of objects. >> > 1998 S70 - so it's the new stuff >> > plenty of freon though ~40# per mechanic [quoted text clipped - 24 lines] > > Bob Am I the only one kicking himself for missing that? Mike > Am I the only one kicking himself for missing that? > > Mike Well, my '98 S70 only takes 750 grams = 1.65 lbs = 26.4 oz. So 40 oz. would be way too much. Also, they put the expansion orifice (not valve) in the high pressure (or liquid) line more than a foot from the firewall to reduce the hissing noise inside the cabin. So both lines can be covered in frost from this point to the firewall. SignatureMike F. Thornhill (near Toronto), Ont. Replace tt with t (twice!) and remove parentheses to email me directly. (But I check the newsgroup more often than this email address.) |
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