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1991 740 A/c issues

12372 Views 7 Replies 3 Participants Last post by  Joseph/TX
Allright I have searched the forums and come up empty. I have 91 -740 Turbo. Where is the mysterious "relay" mentioned in the Haynes manual that turns the darn A/C on?

I have jumpered the power wire to the compressor and it turns on and runs just fine! Bad news is, it doesn't get cold. ( Ok so I must have a leak too :)-( ) Jumping the low pressure switch does not turn it on.

I have pulled out the control panel and found that the A/C button activates a micro switch in the vacumn line area. According to the wiring diagram there is a delay relay somewhere, but it is not in the relay bay.
Can anyone please tell me where it is?

What else could cause the power to the compressor to fail to get there?

The Volvo dealer thought the compressor was frozen, not the case!

Vacumn leak? Separate vacumn pump for the A/C?

Same problem with the cruise control. Does not activate. The wiring diagram again shows a mysterious brain box and vacumn pump for it.

Where are they!!!???

I'd like to help my 82 year old father out, but am getting nowhere with the repair manuals or the dealer.

Any advice/expertise with these issues would sure be appreciated!

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Have you tried changing out the switch with another one to see if that is the issue? Here is a link on Volvo relays that may also help you out.

Volvo Relays
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