ascMcLaren Enthusiasts

Hi all - finally got around to working on my A/C. I have detemind by the fittings that it has been converted (I hope).

First - Bought a can of freon with a gauge and attached it. very low pressure (< 5). So I added freon per the instructions. Got it up to about 45. Still no go.

Second - checked power to compressor - 12 Volts sometimes. Added a little more freon. Clutch started cylcing couple seconds on, a few seconds off.
Third - while cycling, compressor started - pressure dropped to about 25, stopped. Came back up to about 40-45 - started and then pressure dropped again and stopped.... repeat.

I checked the wiring to the pressure switch. Seems OK. I can feel the switch click when clutch engages/dis-engages. Is it possible that the switch is bad?? A $20 part so I may try to change it myself.

I was wondering what the normal pressure range is while operating. Any thoughts ?? Is 25 to 45 range corrcet switching range for this switch?? If so, I may have a bigger problem. Gee...I hate these intermittent things!!!

Thanks -Dwight

You need More freon. It should run more than a minute between cycling. Being low, it just depletes the low side pressure and cuts out the switch.

That's why you jumper the switch to keep it going. When it's full you will have about 40f at one vent.

svo413 wrote:You need More freon. It should run more than a minute between cycling. Being low, it just depletes the low side pressure and cuts out the switch.

That's why you jumper the switch to keep it going. When it's full you will have about 40f at one vent.

OK - I'm a bit dumb about this. Why does the low side go right back up when the compressor stops? Should I jumper the switch while I'm filling it and keep an eye on the low side pressure?? At some point, will it stop cycling??

THANKS !!!!

Yes and yes. It will take a while. You are filling with gas. It uses liquid in parts of the system. It's like filling a beer glass using a spoon and usung just the foam head.

svo413 wrote:Yes and yes. It will take a while. You are filling with gas. It uses liquid in parts of the system. It's like filling a beer glass using a spoon and usung just the foam head.

Great !!! I'll give it a try tomorrow.

THANKS AGAIN !!!!!!

That would certainly an advantage and benefit at the same time for you..For sure..!!
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Bat rolling

Wel....I tried again today. Jumpered the switch and pumped a little more freon in. No go. While running, the pressure dropped to zero and stayed there. Kept adding freon. I then pulled the jumper and the pressure jumper very high - like I put in too much freon. never got any cold air.

I talked to my mechanic and he thinks I have air in the system that could be causing the trouble. He thinks I should have it evacuated and he will try again. At this point, I don't want to make things worse so I will probably do that. Given that I don't know how long this has not been working, proabably a good idea anyway,

Dwight

Sounds to me like you have a restriction maybe the orifice tube is clogged, how high is it with the jumper off or car off, how low does it go when you jumper it?

Yes, you need to do what your mechanic says. Evacuate everything and then add enough coolant as per the manual. If you can't get a good vacuum in the system, that will require some looking as to what is leaking. I would replace all o-rings while you have it apart.

I went to Harbor Freight and bought their AC manifold gauge set. It works very well (cheap too, like $50 with a 20% off coupon you can google) and you can watch the high and low sides of the AC system.

Harbor Freight also sells a $15 vacuum pump that uses your compressor to create enough vacuum to evacuate an AC system.

The last piece you need is an AC coolant tank. You can get one for about $80 on Amazon...but I'd love to know if there is a cheaper source (then I'd be all set with that).

The manifold gauges are definite requirement if you plan to have older cars with AC around. You really need to know the high/low side pressures and see where and when it cycles.

The correct pressures are very dependent on the current ambient temperature of the outside air, so it's hard to say exactly what pressure should be in the system. This is why manuals will only say how much coolant should be in the system, never pressures. The only way to know how much coolant is in the system, is to evacuate it all and put in exactly what the manufacturer states should be in it.

People experienced with the particular AC unit can probably give you a pressure range at a particular temperature but you won't find it in a manual (at least I couldn't find it for the Honda I was working on).

-Mike

There are pressure vs air temp charts in the factory manuals. If you are converted to r134a then there are no specific tables but a generic pressure for a given air temp. Someone quoted something on Fep a couple weeks ago like 80 plus the air temp foe r134a.