On a 1991 W126 firewall? I just replaced the fuel pump relay and I'm thinking that I should also replace whatever that other one is to preempt any problems.

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1991 560SEL (254K miles)
1980 Lincoln Mark VI - Givenchy
1979 Lincoln Mark V Collector's Series
1979 Lincoln Town Car Collector's Series
1979 Ford "Effie" Pickup (in gradual transformation to a show/street truck)
1969 Lincoln Mark III (waiting for "Overhaulin" to call)
1989 Lincoln Towncar
2001 Lexus GS300 (spousal unit's daily driver)

The one next to it is marked 'Klima' and controls the air conditioning/ventilation in your car. There's no indication on this board that this is a high failure rate part, so I would suggest if you a/c works well that you save your money.

If the relay fails, your car will still run to the local dealer where you can get ripped off for a new one - or buy from FastLane and wait a few days.

Thanks TP:
Is that the relay for the blower function or for the cooling function? My A/C only blows cool at highway speed. Maybe that's a reason?

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1991 560SEL (254K miles)
1980 Lincoln Mark VI - Givenchy
1979 Lincoln Mark V Collector's Series
1979 Lincoln Town Car Collector's Series
1979 Ford "Effie" Pickup (in gradual transformation to a show/street truck)
1969 Lincoln Mark III (waiting for "Overhaulin" to call)
1989 Lincoln Towncar
2001 Lexus GS300 (spousal unit's daily driver)

You may have a blown mono-valve - it sits in the little cube to the left of the two relays you mention under an alloy cover retained by four screws with an electrical connector on top. More or less in line with the passenger's seat.

Check this forum using the search function - an easy DIY replacement and about $30. With the engine cold take the top off and pull out the valve - a slender stick-like thing. Check if the rubber diaphragm on it is torn. Is so, replace - ~$30. If it's OK, suspect your relay.