98 Grand Caravan A/C control head

[ggrieves]

Recently purchased this 98 Grand Caravan. The A/C would only cool part of the time, usually just a little right after the engine was started. The seller said he had a mech check it out, (did not run any actual diagnostics) The A/C button would not stay pushed in or light up on the controls so he suggested that the control head might need replaced. I had a buyers check done and the mechanic who checked it out said the same thing; possible bad control head. I purchased a used control head and it lights up, actually four of the selections flash on and off. I found a repair guide in the van that said when replacing the A/C control it would need calibrated. My question is, can anyone tell me how to calibrate/reset the control head? I had a can of freon put in the unit in case the a/c was only cooling part of the time because it was low on freon and that mech said the compressor was staying on all the time. There was a language barrier, he did not speak much english, but I think he said that it could use more freon. I will need to check that out again but right now I need to get the control working. Any help would be greatly appreciated.

[marc-o-matic]

Engine idling,blower on high,mode switch to panel,temp lever full cold.
Press and hold rear wipe and wash buttons simultaneously for 5 seconds
untill all led's illuminate.
Rear wiper and intermitent wiper led's will flash during calibration.
Also a/c and recirc. butons will flash alternately during test.
After about a minute if only rear wiper led is flashing system calibration is successful.

HTH

[webbch]

Don't just go adding refrigerant willy-nilly. You don't just add the "cold stuff" and automatically have good cooling. There is an optimum amount to be in there, too much or too little are both bad things. The only effective way to know how much is in there is to evacuate and recharge by weight. At that point, a manifold gauge set for reading both high and low side pressures will become a useful diagnostic tool. Without some knowledge of the quantity of refrigerant, system low/high pressures may be misleading, even if "within spec". There are ways of charging by pressure, but that's an iterative process where you add a little and look at the pressure response, add a little more, etc. Much faster and easier to charge by weight, if a weight spec is available, which in your van is 3.00 Lbs if you have rear air, and 2.88 Lbs (IIRC) if you don't.

Regardless, as mentioned, the a/c light should be on when you press it in, so that is probably the first thing to fix as you seem to already know. Just a cautionary statement about adding refrigerant.

FYI, not trying to critisize, but freon is the trade name given to R-12, in much the same way that Formica is the trade name for a plastic laminate. Obviously, your van uses R-134a.

[ggrieves]

Originally Posted by marc-o-matic

Engine idling,blower on high,mode switch to panel,temp lever full cold.
Press and hold rear wipe and wash buttons simultaneously for 5 seconds
untill all led's illuminate.
Rear wiper and intermitent wiper led's will flash during calibration.
Also a/c and recirc. butons will flash alternately during test.
After about a minute if only rear wiper led is flashing system calibration is successful.

HTH

Thanks! Thats what I need to know. I will have to wait till this weekend to try your suggestion. I bought the car for my daughter and she lives in another city. I will let you know how it goes

[ggrieves]

Originally Posted by webbch

Don't just go adding refrigerant willy-nilly. You don't just add the "cold stuff" and automatically have good cooling. There is an optimum amount to be in there, too much or too little are both bad things. The only effective way to know how much is in there is to evacuate and recharge by weight. At that point, a manifold gauge set for reading both high and low side pressures will become a useful diagnostic tool. Without some knowledge of the quantity of refrigerant, system low/high pressures may be misleading, even if "within spec". There are ways of charging by pressure, but that's an iterative process where you add a little and look at the pressure response, add a little more, etc. Much faster and easier to charge by weight, if a weight spec is available, which in your van is 3.00 Lbs if you have rear air, and 2.88 Lbs (IIRC) if you don't.

Regardless, as mentioned, the a/c light should be on when you press it in, so that is probably the first thing to fix as you seem to already know. Just a cautionary statement about adding refrigerant.

FYI, not trying to critisize, but freon is the trade name given to R-12, in much the same way that Formica is the trade name for a plastic laminate. Obviously, your van uses R-134a.

I appreciate what you are saying about adding freon. I have done alot of work on cars but I never learned how to work on A/C systems or even use the gauges when adding freon. I will seriously consider having it vacumed clean and then refilling by weight. Thanks

[webbch]

I see your profile indicates you live in Texas - so you use/depend on A/C enough to possibly make it worthwhile to invest in the tools to work on your own a/c. I've recently done this, and practically speaking, to *really* get set up properly to evacuate and recharge your system runs about $1000-1100, or less than the cost of one major A/C bill. This includes a quality 5 cfm vacuum pump, (used, most likely on ebay, but good one) refrigerant recovery unit, recovery tank, electronic scale, manifold gauge set, instruction manual, 30 lb tank of R-134a and odds and ends for can taps, etc.