Can anyone advise me as to how I can get my stock air conditioning system to blow colder air? I have a 1967 427/390 corvette with a factory installed air conditioning system but the temperature in the ducts seems to be around 70 degrees and, I believe it should be a little cooler than that. The coolant system is R/12 Freon. Any information would be greatly appreciated.
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Re: Air Conditioning
There are a couple of simple things to look for on any A/C system. Without a gauge set connected I would check the following:
1. Is the compressor turning? (Is the clutch engaging when the A/C is turned on?)
2. Is the suction fitting on the compressor cold? It should be COLD, not just cool. Are there bubbles in the sight glass? A cool suction and bubbles in the sight glass indicate that it is low on charge. A warm suction and no bubbles indicate that there is no charge or the compressor is not pumping. The suction fitting should be cold and there should be no bubbles in the sight glass when properly charged with R-12.
3. If #2 is OK then there is a good chance that the expansion valve has problems. Either not working or frozen from moisture in the system. At this point you will need to have someone that knows what they are doing work on it. I would put the gauges on it and look at the suction and discharge pressures. They would probably show no flow through the expansion valve so I would start by evacuating the system to dry it out, refill it, and try again. This probably won't work so the next step is to change out the expansion valve. Purge the system again, remove the evaporator, replace the expansion valve, reassemble, refill, and try again.
good luck,
Dave Christensen -
Re: Air Conditioning
You copy of the '67 Chevrolet Chassis Service Manual should provide a nice table in the air conditioning section that details what outlet temperature(s) you should expect, by Chevy model, vs. exterior ambient condition (temp, altitude, Etc.). You'd use this to test/verify proper system performance. BUT, it's important to let the system run and come to steady state since when you first begin the cooling process, the A/C has to swamp BTU's out of the Harrison heat exchange box and this can take a while (perhaps 5 minutes or so). So, it's important to determine the outlet temperature you're measuring is really the system's steady state vs. an arbitrary start-up reading.
Based on the performance table, you should find an expectation of high 30F to mid 40F outlet temperatures defined for your car. This is a FAR cry from the 70F you mention and IF that observation truly is a steady state reading, there ARE system efficiency problems to hunt down and correct. These would include:
(1) Low refigerant level
(2) Compressor worn/not efficiently pumping
(3) Blocked refrigerant passage ways
(4) Faulty throttle valve
(5) Obstructions to air flow (leaves & debris) through the evaporator core
(6) Same for the condensor & radiator including bent fins
(7) Worn/slipping compressor clutch and/or improper air gap setting
(8) Worn/plugged receiver dryer
Many of the above conditions can be diagnosed by a competent automotive A/C technician with classic car experience using the CSM book's performance tables and properly connected inlet/outlet pressure monitoring gauges.Comment
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Re: Air Conditioning
Hi Peter,
Another item often overlooked is the water control valve. It is designed to shut off the hot water flow in the heater core when you are in the A/C mode. Since the heater core and evaporater share the same enclosure the valve needs to be closed in the cooling mode.
Page CampbellComment
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Re: Air Conditioning
Peter once up on a time when I was away on business back in 88 my wife took my 70 to the Chev dealership to get the air fixed becasue it was not cooling. The dealership techs wanted to replace the evaporator and would have if they could of untightened the connections. (I am glad they could not.) The car left the dealership without blowing cold air. Using my service manual I was able to discover the problem. The desiccant bag in the dryer had ruptured and the dissicant was blocking the flow of R-12 in a filter screen just like it was designed to do. I don't have my service manual handy right now, but I believe the part is the expansion valve that has the small screen on the inlet line. This valve has a removable filter screen (a real wire screen that is removable and can be cleaned and reused) that was stopped up with the desiccant. I installed a new dryer and cleaned the lines the best I could, replaced the filter screen with a new one, and had it professionally vacuumed down and recharged with R-12. Its still cooling today. A shop that that still has the R-12 equipment can recover your R-12 so repairs can be accomplished and not lose the R-12.Comment
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Re: Air Conditioning
Page I don't know specifically about the 67, but my 70 has 4-season air conditioning and the inline valve in the heater hose supply closes off the flow of hot coolant only when on "MAX" air conditioning selection.Comment
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Catch-22
Most States require automotive tech's to recover R12 from a system, but then PROHIBIT them from reusing the original refigerant! That means they WILL suck your system dry, but when it comes time to refill it, be prepared to BEND OVER for the $40-60/lb price for freshly recycled R12, and, no they don't measure and give you 'credit' for the amount of original R12 they 'mine' out of your vehicle....Comment
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Re: Air Conditioning
If you take it in to a shop. Don't settle for just a recharge or topping off the system. Unfortunately it seems many shops just recharge the system and call it fixed. A few months down the road, you'll likely be in the same shape except much poorer due to the expense of R-12. It will cost more, but you may need to replace the old hoses and the compressor seals, and dryer. But it should not be a perpetual problem.Comment
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Do You Have A Manifold Gauge?
If not, then you are only guessing. There are tables to indicate high side/low side pressures @ indicated RPM/ ambient temp values. Unless you know for sure that there is nothing else wrong with your system, then the easy way to get more cold air is by adding R12 (R132a). It is hard to say---you may have had a massive leak, in which case, you will need to evacuate the system, purge or replace your reciever/drier core, replace the compressor oil, find/fix the leak, and recharge with new refrigerant. The availability of R12 is very limited these days. If your system is seriously depleted, then it would be wise to look into retrofitting your system to run with R132a medium.
JoeComment
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