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Roamer37 · 06-22-2022, 01:35 PM

We have our 1999 Discovery 37V at a truck shop for AC work. The dash AC gradually stopped working last year. I found an AC hose fitting that was leaking. They put a new o-ring in it and charged the system. The compressor will not turn on. They ran power to the compressor directly and it started up and blew cold air. He said the pressure on the high side was 375 and the compressor needs 300 to run. They cannot figure out why it won't start up.

Does anyone have any suggestions on this? Thanks!

Blackmonltc · 06-22-2022, 01:40 PM

Does the dash light come on? If not it is fuse. Also there is a fuse I’m line back where the compressor is .

jacwjames · 06-22-2022, 01:50 PM

Pressures seems high but each system is different. It also dependent on temperature. I'd do some checking on this as too much pressure isn't good.

hayward3411 · 06-22-2022, 01:54 PM

As stated above the dash light must be on in order for a signal to be sent to the compressor to energize.
My Fleetwood Expedition had 2 low voltage fuses (5v) located under the dash, they were very difficult to locate. Once replaced the dash light came on.

Good Luck

Roamer37 · 06-22-2022, 01:55 PM

The green dash light comes on when the AC button is pushed. The system had been working perfectly until the 134a leaked out at the bad hose fitting.

Tha_Rooster · 06-22-2022, 02:09 PM

Quote:

Originally Posted by Roamer37

The green dash light comes on when the AC button is pushed. The system had been working perfectly until the 134a leaked out at the bad hose fitting.

If you have a low pressure cut out switch have you straight wired it to see if compressor kicks on?

Roamer37 · 06-22-2022, 02:10 PM

Quote:

Originally Posted by Tha_Rooster

If you have a low pressure cut out switch have you straight wired it to see if compressor kicks on?

Yes he wired it direct and it started and blew cold.

Ledawg · 06-22-2022, 02:14 PM

I had this same problem on my 07 Southwind. I found the problem by accident. It turned out to be a bad connection in the kick panel that covers the blower motor up front. (Ford chassis for me) I unplugged a connector and plugged it back in and it worked. I couldn't figure out what I had done when it started working. I had to set and think about what I had changed. The connector was to the high pressure switch I believe that is in the condenser box,

Blackmonltc · 06-22-2022, 02:20 PM

Had this problem on my 2003 Discovery. Had a bad connection where the ac compressor plugged in at wiring in back top of engine.

Tha_Rooster · 06-22-2022, 04:07 PM

Quote:

Originally Posted by Roamer37

Yes he wired it direct and it started and blew cold.

Direct to compressor or low pressure cut out switch?

Roamer37 · 06-22-2022, 04:17 PM

Quote:

Originally Posted by Tha_Rooster

Direct to compressor or low pressure cut out switch?

Direct to compressor I think.

twinboat · 06-22-2022, 05:38 PM

The capillary tube thermostat is in series with the power to the compressor clutch.

If the capillary tube is cracked, the fluid leaks out and the switch stays open.

Old Scout · 06-22-2022, 05:57 PM

Systems vary but it takes much less than 300 psi to allow compressor to start. However, 375psi on a circa 1999 system would likely be too high [see below]. Since they "cracked" the system open, did they replace the filter/dryer? Most systems have a trinary switch near the dash--it senses hi and low 134a pressure. There is also a freeze tube on the evaporator. So, fuses. connections or sensors could be the issue.